Desalination method and system using compressed air energy systems

ABSTRACT

The invention relates to a desalination method and system that uses freeze crystallization technology that incorporates the use of compressed air energy as the source for freezing temperatures. When compressed air is released by a turbo expander, chilled air is produced as a by-product, wherein the chilled air is introduced into a crystallization chamber. Also injected into the chamber is a spray cloud of seawater droplets, which has been pre-chilled by heat exchange with the cold chamber walls, and which is then circulated and exposed to the chilled air in the chamber. The sizes of the droplets can vary, but are preferably predetermined, along with the relative temperatures, flows and speeds of the spray and chilled air, such that when the droplets are circulated within the chilled air, and settle at the bottom of the chamber, they are deposited at slightly above the eutectic temperature. This way, the ice/snow mass that forms at the bottom of the chamber will consist of frozen ice crystals, and a residue of salt water brine, which can runoff from the mass, either from the sides, or through any voids or channels that may form within the mass.

RELATED APPLICATIONS

The present application claims the benefit of the filing dates of U.S.Non-provisional patent application Ser. No. 11/585,023, filed on Oct.23, 2006, and U.S. Provisional Patent Application Ser. Nos. 60/832,777,filed Jul. 24, 2006; 60/794,190, filed Apr. 21, 2006; and 60/789,415,filed Apr. 5, 2006. All of these applications are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the field of desalination systems, andin particular, to a desalination system that uses compressed air energythat can be released and expanded to co-generate chilled air, which inturn, can be used to freeze water, and produce fresh drinking water.

BACKGROUND OF THE INVENTION

In the United States, where there is a broad range of climate zones, andan abundance of rain in many areas, there is typically an adequatesupply of fresh drinking water available in most regions of the country.Even in areas where water supplies are scarce, efforts have been made totransport water from where it is available, to where it is needed. Forexample, a significant amount of water is currently being transportedfrom the Colorado River, via the California Aqueduct, to heavilypopulated, but dry, regions of Southern California, so that sufficientwater will be available, not only for drinking purposes, but also foragriculture and irrigation. Other means of supplying and transportingwater, such as through a network of utilities and pipelines, includingthose from lakes, reservoirs, rivers, glaciers, etc., are also inexistence.

Nevertheless, there are many geographical areas where it is not asconvenient or possible to transport water to where it is needed, on acost effective basis. These areas include far away regions in themountains, faraway rural areas, and islands in the ocean, where it mightbe cost prohibitive to install long pipelines or aqueducts to transportwater to those areas. There is also a need for fresh drinking water onboard ships, such as those that go for extended periods of time, i.e.,cruise lines, ocean liners, cargo ships, Navy fleet ships, etc. Thereare also other countries, such as where the climate is drier, or wherethe population is much larger than the availability of fresh drinkingwater can support. Ironically, many of these areas are located close tothe ocean, or other salt water bodies, where seawater is available, butwhere the amount of fresh drinking water available may be insufficientto meet the demand.

Accordingly, desalination systems and methods to produce fresh drinkingwater from seawater have been developed in the past. The key to anydesalination system is the ability to separate the contaminants,including salt and other impurities, from the base water, which, inturn, can produce fresh drinking water.

For purposes of simplicity, the term “seawater” will be used from thispoint on to refer to any contaminated water that needs to be purified,whether it is actually water from the sea, or brackish water, or anyother water from any other source.

At least three different types of desalination systems are currently inuse today, to varying degrees of success, which will now be discussed.

Thermal Method: A thermal method is one that uses heat or other means toconvert the seawater into a water vapor, such as by boiling, leavingbehind the contaminants in the residual base water. For example, onetype of thermal method commonly used is called distillation, whereseawater is progressively heated in subsequent vessels at lowerpressures to produce a purified water vapor.

The thermal method called Multistage Flash Distillation is the mostcommon desalination method currently being used world-wide. It involvesheating the seawater to a high temperature and passing it through aseries of vessels having decreasing pressures to produce water vapor.The heated water is passed to another vessel known as a “stage”, wherethe surrounding pressure is lower than in the heater. The suddenintroduction of solute and water into a lower pressure “stage” causesthe solution to boil so rapidly that it flashed into steam (watervapor). The water vapor, by its very nature, consists of purified freshwater without the solutes, which can then be condensed, collected andused for drinking water. A similar process called Multi-EffectDistillation uses the same principles as the Multistage FlashDistillation, except that this method operates at lower temperatures. Atlower pressure there is a lower temperature required to vaporize a givenweight of water. There is also another distillation method called VaporCompression Distillation which is generally used in combination withother processes, where the heat comes from the compression of vapor,rather than direct exchange of heat.

While these methods are highly successful and effective in being able toremove contaminants from the seawater, one of the most significantdisadvantages of these methods is the high cost of operation, includingthe high cost of the energy needed to heat the seawater, and/or reducethe pressure, to boil it. Because of these costs, these methods areoften used only when fresh drinking water is not available, or could notbe made available at a lower cost.

Membrane Processes: A membrane process is one that uses a relativelythin permeable layer of material that allows either water or salt topass through, which helps induce a separation between two differingconcentrations. On one side of the membrane is typically located thewater with the contaminants, and on the other side of the membrane istypically located the water that has been purified.

One of the most common types of membrane processes is reverse osmosis,which is a pressure driven process which forces saline water through amembrane, leaving salts behind on the other side. While reverse osmosishas been shown to be economical in terms of its relatively low energyconsumption rate, the process typically has a significantly higherupfront investment cost compared to most thermal methods. There is alsoa relatively high cost associated with the replacement cost of membranematerial, due to limited membrane life.

Another common membrane process is called Electrodialysis, which is avoltage driven process that uses an electric potential to move saltsselectively through a membrane, leaving fresh water behind. This processhas some of the same drawbacks as reverse osmosis, in that the upfrontcapital costs can be prohibitive.

Freeze Crystallization: Freeze crystallization is a process which takesadvantage of the freezing process and the phase diagram of seawater toproduce fresh drinking water. Essentially, seawater is subjected tocooling temperatures, such as via a refrigerant, which causes freezingto occur, wherein the freezing is used to help form solid ice crystalsmade from pure water, which can then be separated from the saltcontaminants contained in the residual base water. This process and itspotential has been investigated due to its higher efficiencies whencompared to reverse osmosis, but the freeze process for desalinationpurposes has never been implemented successfully on a large scale.

The freeze crystallization process is different from the otherprocesses, and typically involves the formation of ice crystals byfreezing seawater, wherein the pure water ice crystals can be separatedout of the base water. During the process, when pure ice crystals areformed by exposure to freezing temperatures, they are usually allowed totraverse to the top of a tank, under action of buoyancy, while theimpurities are allowed to separate and sink by reason of a higherdensity. This way, it is possible to separate the pure ice water fromthe impurities, such as the salty brine and other minerals, whereinfresh drinking water can be produced.

In addition, the formation of ice crystals, in this respect, can beachieved in two different ways: 1) by direct cooling, and 2) indirectcooling.

Direct cooling involves using an inert cooling fluid or refrigerant thatis physically injected into the seawater, i.e., bubbled through it,which causes the seawater to vaporize at the desired temperature. Thisis the result of the refrigerant heat of evaporation being drawn fromthe solution, which causes the seawater to cool down to the eutectictemperature. Although the intermixing of the refrigerant with theseawater makes this method efficient, an important drawback is that therefrigerant ends up getting disadvantageously intermixed with the ice.That is, ideally, the process would form distinct particles of purewater ice, but in this cooling method, some of the refrigerant, which ispresent throughout the equipment, ends up being trapped within the iceparticles, and therefore, fresh drinking water, free of the refrigerant,cannot be produced with purity. Consequently, the direct cooling methodhas not been used in connection with the production of fresh drinkingwater.

A more common freezing desalination process is called indirect cooling.In this process, the refrigerant is not injected directly into theseawater, but rather, is introduced into a series of pipes or jacketsthat run through the seawater. The pipes and jackets are typically madeof a material, like aluminum, with good heat conducting properties, andhelp keep the refrigerant and seawater separated during the process. Therefrigerant preferably only passes through the inside of the pipes andjackets; the seawater, on the other hand, is only exposed to theexterior of the pipes and jackets, and not the refrigerant itself. Thisway, the seawater is cooled by direct contact with the pipes andjackets, and not direct contact with the refrigerant. This avoids theproblems associated with the direct cooling method, although using pipesand jackets introduces an added level of resistance to the transfer ofheat from the seawater to the refrigerant, which makes this method lessefficient.

Once the pipes and jackets are cooled, and seawater is passed over them,ice crystals are formed on the exterior surface, and therefore, itbecomes necessary to remove the ice from the surface physically, such asby using a scraper. Once the ice is physically removed, the lowerdensity ice crystals that are released tend to float to the top of thehigher density brine solution. This way, the ice crystals can be removedfrom the top, and washed clean of impurities, and then allowed to thawand melt, wherein they produce purified drinking water. Thereafter, thesalty brine mixture can be disposed.

The total surface area of contact that is needed for indirect coolingand the heat transfer coefficient are the key parameters of thisprocess. These parameters relate to the effectiveness of the refrigerantin being able to cool and freeze the seawater solution around therefrigerant-containing pipe or jacket.

An example of an indirect cooling method in use currently is called aScraped Surface Crystallizer, which consists of a cooled cylinder(evaporator) with a knife or scraper arrangement that is able to scrapeice crystals off of the cooled surface. Either the scraper moves overthe cooled surface, or the cooled surface is moved across the scraper,to enable the ice to be scraped and removed. In either case, to avoidfriction and damage to the surfaces, the system is typically designed sothat there is a clearance or gap between the surfaces, which ultimatelyleaves behind a layer of ice on the cooling surface. This additionallayer of ice on the cooling surface causes the entire system to beinefficient in its ability to transfer heat away from the coolingsurface, to allow more ice to be formed on the surface, and causes asharp decrease in heat flow through the cylinder, and a drop in itscapacity. There is also the adhesion force that exists between thescraper and the cooling surface which requires the expenditure of energyto overcome, i.e., extra energy is needed to scrape the ice to remove itsuccessfully, and this must be accomplished constantly over an extendedperiod of time.

There have also been studies done involving freezing wastewater todetermine how ice crystals form within a droplet. In studies by Dr. WaGao, discussed in her thesis entitled “Partial Freezing by Spraying as aTreatment Alternative of Selected Industrial Wastes,” the effect offreezing temperatures on a single droplet of wastewater was studied,wherein a single droplet (at below freezing temperatures of fresh waterof about minus 5 degrees C.), was exposed to an updraft of subfreezingair temperatures, i.e., between minus 5.5 degrees C. to minus 17.7degrees C., in a chilled air vertical wind tunnel. The test wasperformed repeatedly for the same droplet size and droplet condition toobtain statistical information. She observed the freezing of eachdroplet began at the bottom edge of the droplet, and then enveloped theouter surface area of the droplet in 0.23 seconds. The wastewater frozeinwardly as the ice shell thickened. The complete 2,800 micron dropletfroze completely in a mean period of time, i.e., 7 seconds. In all casesthe freezing was complete in 20 seconds. The solid ice portion of thedroplet was formed with pure water, and the remaining liquid brinearound it consisted of the concentrated wastewater. The ice spheresfragmented during the freezing process as the interior liquid brine wassqueezed to the outside because of internal stresses in the ice as itsqueezed the incompressible liquid. In another study, wastewater wassprayed outdoors in cold arctic winter weather to produce a large moundof ice particles directly on the ground. Although initial freezing tookplace while the droplets were in flight, additional freezing andseparation occurred after the droplets landed on the ground. Once themound was formed, it could then be melted during the spring, and usedfor irrigation purposes.

Because of the drawbacks of the existing desalination methods andsystems discussed above, there is a need for a highly efficient and costeffective desalination method that allows fresh drinking water to beproduced from seawater.

SUMMARY OF THE INVENTION

The present invention relates to the use of compressed air energy inconjunction with a water desalination system, wherein energy produced bythe wind, or any other energy source, can be used to produce compressedair, and wherein when the compressed air is released and expanded, suchas by the use of a turbo expander, it can produce dramatically chilledair, as a by-product, which in turn, can be used to freeze anddesalinate seawater. That is, rather that using a refrigerant to reducethe temperature of the seawater for desalination purposes, as in thecase of the freeze crystallization methods described above, the presentinvention uses clean chilled air, derived from releasing and expandingcompressed air energy, directly mixed with the seawater droplets, toproduce fresh frozen ice particles.

Overall, the approach is to abandon the reverse osmosis method ofdesalination, and use a freeze crystallization process that works at theatmospheric pressure and at the low heat of ice fusion, rather than atthe atmospheric pressure and high heat of evaporation, as in the case ofthe Multistage Flash Distillation method.

The approach generally comprises the following steps:

-   -   1. Producing a volumetric flow of chilled air at temperatures as        low as minus 175 degrees F. at slightly above one atmosphere of        pressure, and introducing this chilled air into an insulated        mixing chamber. This chilled air can be accomplished by        expanding the compressed air, which is produced by a compressor,        through a turbo expander to produce chilled air directly, or        through a turbo expander and generator that produces electricity        and chilled air as a by-product.    -   2. Producing a volumetric flow of seawater which can be sprayed        as a droplet cloud into the chamber and mixed with the chilled        air to cause the temperature of the seawater droplets to be        reduced to at or slightly warmer than the eutectic temperature,        which for regular seawater is about minus 6.2 degrees F.    -   3. As the seawater droplets begin to mix with the chilled air,        and freeze, due to heat exchange, pure water ice crystals begin        to form, which begin to separate from the salty brine solution.        Over time, i.e., less than a few seconds, the frozen ice        particles begin to fall to the bottom of the chamber, where due        to heat exchange the temperature of the air is warmer, and        wherein the air and the growing deposit of ice particles at the        bottom eventually reach an equilibrium temperature that is        preferably just above the eutectic temperature. Then, the lower        density ice particles begin to float and coalesce on top of the        higher density salty brine solution that collects at the bottom,        and form an ice/snow mass that continues to enlarge and float on        top of the salty brine solution, wherein any higher density salt        brine continues to separate from the ice particles and runoff        down the sides of and through the channels and voids that exist        in the ice/snow mass. A fresh water wash column involving a        spray of water can be used to help facilitate the runoff of the        brine from the ice/snow mass to help clean the ice mass further.        Note: The density of the brine may be between 1.35 gm/cc when        concentrated and 1.025 gm/cc in seawater; whereas the density of        pure water is 1 gm/cc; the density of fresh water ice is 0.917        gm/cc; and the density of snow is less than 0.1 gm/cc. Thus the        high density brine flows out between the pores in the ice/snow        mass and over the interstices between the ice fragments.    -   4. At the end of the cycle, which is after the ice/snow mass is        formed, the ice/snow mass is preferably removed, and then        allowed to thaw and melt, wherein purified drinking water can be        produced. The salty brine solution becomes more dense and salty        over time, and is removed from the chamber, along with any salt        solids that are formed, so that the process can begin again. The        deposited salt and other minerals can be saved for later        industrial use or must be properly handled when disposed.

The present invention preferably contemplates using the expansion ofcompressed air as the source of freezing temperatures to freeze anddesalinate seawater. There are at least three different methods ofproducing chilled air contemplated, as follows: (1) a compressed airenergy storage system having a compressor and a large high pressurestorage tank, wherein a turbo expander is used to release and expand thecompressed air when it is needed, wherein the energy produced isconverted into chilled air and/or electrical energy, (2) a turboexpander having the dual capacity to generate electricity and chilledair, wherein the electricity generating capability is preferablyreplaced by a supplemental compressor capability that uses the turboexpander work to replenish the discharged compressed air in anassociated surge tank, and (3) a turbo expander having the capacity toproduce chilled air without having to store the energy first. In eachcase, the chilled air is injected into the mixing chamber to providecooling for the seawater that is injected into the chamber.

The present invention preferably comprises a desalination system thatcan be performed in batches, inside a mixing chamber, wherein a mass ofice/snow made of fresh water is formed, and then removed from thechamber, and allowed to melt, to form pure water. To form each batch,the seawater and chilled air in the chamber must be properly mixed, andtherefore, the seawater is preferably pressurized and passed through anarray of nozzles, to form a spray of droplets, or cloud. By injectingthe chilled air into the mixing chamber so that the sprayed seawaterdroplets is exposed and circulated with the chilled air, ice crystalswill begin to form within each droplet. The volumetric size of eachseawater droplet and the temperature of the seawater and chilled air fedinto the chamber are preferably carefully predetermined, as well as theoverall size and configuration of the chamber. Also preferablypredetermined is the manner in which the seawater spray and chilled airare injected into the chamber, and mixed, to ensure that the resultantmixture quickly reaches the optimum temperature for freezing anddesalination.

Typically, in connection with a seawater droplet, the freezing occursfrom the outside to the inside, but over time, the ice structure that isformed forces the saltwater brine to the outside, i.e., brine rejection.It has also been observed that the ice shell around the concentratedbrine core develops internal stresses and the ice shell fragments andforces the concentrated liquid brine to the outside of the ice shell.The agglomeration of ice crystals, which forces brine away, eventuallyforms an overall structure that has the ice crystal as a monolith, whichin turn, is coated with brine. When these coated ice crystals impinge oneach other, the brine solution is forced to surround the newly formedice crystal composite. This process continues until there is a completeseparation of a macrostructure of ice surrounded by brine. At the bottomof the chamber, the final ice mass that forms appears like porous snowthat permits gravity drainage of the brine. As will be discussed,additional fresh water can be added to further release any brineattached to the ice. And, the fresh water that performs this function offreezing and releasing more brine can be recovered again for reuse.

The direction of the seawater spray and chilled air being introducedinto the chamber can contribute to the proper formation of the icecrystals and therefore the ice mass. In this respect, the presentinvention contemplates both a 1) counter-flow and 2) co-flowarrangement. The factors that determine which to use depends on howquickly the seawater needs to be frozen, which is dependent on how coldthe seawater is before it enters the chamber, how cold the chilled airis, the size of the chamber, how the seawater droplets are exposed toand circulate with the chilled air, and the amount of each that is beingintroduced, etc.

In the counter flow embodiment, the system preferably has a chamber thatsprays droplets of seawater downward into the chamber, and which enableschilled air from the turbo expander to be blown upward against thefalling droplets, thereby causing the seawater droplets to circulate andfreeze, and then fall to the bottom of the chamber. This is referred toas a counter flow process because the seawater spray and chilled airflow in opposite directions to increase the residence time of thedroplets in the chamber. In another embodiment, the system preferablyhas at least one spray nozzle that sprays droplets of seawater downwardinto the chamber, but which enables chilled air from the turbo expanderto be blown downward in the same direction as the falling droplets. Thisis referred to as a co-flow process because the seawater spray andchilled air flow in the same direction to permit the coldest air to acton the incoming droplet at the greatest heat transfer rate.

In another aspect, the chamber walls are preferably heated with theindrawn warm seawater and/or heat from the compressed air to keep theice from collecting on the walls, and the ice mass from stickingthereto. When indrawn seawater is passed through the chamber walls, theheat exchange that occurs preferably helps to pre-cool the seawaterbefore it is sprayed into the chamber. Preferably, the seawater is pipedthrough tubes or cavities that wrap around the crystallization chamber,such that the seawater is pre-cooled to near freezing temperatures evenbefore it enters the chamber. That is, the super chilled air that isintroduced into the chamber will have the effect of cooling the chamberwalls, so that by wrapping the tubes or cavities around the walls, andrunning the seawater through the tubes or cavities, they will act as aheat exchanger, to enable the seawater to become pre-chilled. This way,the seawater, once it enters the crystallization chamber, will freezemore quickly, and will drop down to the bottom, where it will continueto freeze and solidify. Preferably, this way, the temperature of theseawater even before it enters into the chamber will be close tofreezing or even slightly colder than the freezing point of distilledwater (0° C. or 32° F.).

Waste heat from the compressors can also be used for a similar effect.That is, around the crystallization chamber, it is desirable to preventice particles from sticking to, and collecting on, the chamber walls,and therefore, one way to use the waste heat is to distribute the heatedcompressed air, or warm water produced by the waste heat, within tubesor cavities extending around the crystallization chamber. In thisrespect, preferably, the tubes or cavities can wrap around the chamber,which is where the ice particles are likely to accumulate. Because thisacts as a heat exchanger, when heated air from the compressor is passedthrough the chamber walls, the compressed air is preferably pre-cooledbefore it is sent to the turbo expander and expanded to produce thechilled air. Therefore, the air that is released by the turbo expandercan be made even colder.

Desalination occurs because the seawater is chilled to near its eutectictemperature (about minus 6 degrees F.), and separates into solid ice(frozen fresh water) and liquid brine (highly concentrated salt solutein water solvent), where the formation of the ice crystal forces thesaltwater out of its structure and then there is a further separationinduced by the strong difference in density at the bottom of thechamber. In this respect, the freezing of the seawater preferably occursin three stages: (1) chilling of the filtered seawater pumped throughtubes or cavities surrounding the chilled crystallization walls (strongchilling effect), (2) chilling of the seawater droplets during theirflight through the chilled air in the chamber (short residence time withchilling of the droplet), and (3) chilling of the semi-frozen dropletafter it has deposited at the bottom of the chamber to form an ice mass(longest residence time).

During the downward flight of the droplet through the chilled air, thedroplet begins to get colder progressively inward toward its center, andeventually, ice crystals will begin to form within the shell of thedroplet. In one example, the droplets that are greater than4,000-microns in diameter may have an interior core portion that is notyet frozen, and droplets that are less than 200 microns in diameter maybe completely frozen through to its center.

It has been observed that even if all droplets are the same size, somewill freeze late and some will freeze early because of the process ofhow ice forms around a microscopic nuclei that varies in number andsize, in each droplet of the same size. Note that droplets above 8,000microns in diameter tend to shatter in a relative wind and break up intosmall droplets. Thus the ice layer around a large droplet (defined as4,000 microns in diameter or more) will fragment during the growingthickness of the ice layer around the liquid core. In experiments usingchilled air at minus 17 degrees C., and chilled seawater droplets atplus 5 degrees C., and with suspended piggery wastewater droplets having4,200, 3,400 and 2,800 microns in diameter, it was found that thecomplete droplet was nearly frozen in the mean time of 7 seconds forpH=7.1 (neutral), and 7.5 seconds for pH=11 (alkaline limit is pH=14),whereas there was about 2.5 seconds residence time in flight. Thus muchof the freezing can occur after deposition of the droplet at the bottomof the crystallization chamber. The surface shell of the droplets frozein much less time, i.e., as low as 0.23 seconds.

It is important for the droplets to freeze to form a two-phase solutionof solid ice particles and liquid brine, so it is desirable for thedroplets to reach at or near the eutectic temperature while in flight.On the other hand, if the droplets become too cold (colder than theeutectic temperature) as they fall through the chamber, the fresh waterwithin each droplet could freeze together with the solid salt crystalsand solid brine, in which case, it may not be possible to separate thesalt from the fresh water. This can happen, for example, when theseawater spray consists of varied droplet sizes, wherein the smallerdroplets may reach below the eutectic temperature and completely freezeby the time they reach the bottom of the chamber. In this respect,consider that the spray nozzle that is designed to disperse a cloud ofmean size close to 4,000 microns in diameter will also generate asmaller fraction of mass flow but a huge number of droplets in the rangeof 400 microns in diameter. These smaller particles have a ten-foldsmaller settling velocity and will have a ten-fold longer residencetime. Furthermore, these smaller particles will freeze faster and totemperatures far below the eutectic temperatures when they interact withthe minus 135 deg F. or minus 175 deg F. local air stream exiting thenozzles in the co-low configuration.

Therefore, the small droplets in downward flight through this extremelycold temperature regime will indeed cause undesirable crystallization ofthe droplet into one solid particle composed of (1) Solid ice of freshwater, (2) Solid salt with each salt molecule bound to two watermolecules with attached water molecules, and (3) Solid salt crystals.During the flight of the small particle in the cold air there is noseparation of the brine from the fresh water. However, as will bediscussed, the separation will occur when the droplet deposits on themass of accumulated ice particles created from the large droplets at thebottom of the chamber, which preferably has an equilibrium temperaturethat is warmer than the eutectic temperature.

The very small particle on the order of a few hundred microns indiameter may freeze completely through to their centers when exposed toair temperatures far colder than the eutectic temperature, in the regimeclose to the spray nozzle. When these small droplets deposit on thewarmer ice/snow mass at the bottom of the crystallization chamber, theyare preferably warmed to about the equilibrium temperature of slightlywarmer than the eutectic point. Thus if the small droplets undergofreezing to below the eutectic temperature, they can thaw back up toabove the eutectic temperature. At that point, the usual separation ofthe solid porous snow/ice structure and the liquid salt solution (brine)will occur. Even though typical nozzles spray larger diameter particles,there will always be smaller particles, including a distribution ofparticle sizes within a certain range. The smaller particles are likelyto be large in numbers, but will not contribute to a very large massoverall.

In this respect, it has been found that it is desirable for the ice massat the bottom of the chamber to remain at slightly higher (warmer) thanthe eutectic temperature, such that any remaining salt brine surroundingeach ice particle will drain and runoff down the sides of the ice mass,or through voids or channels formed in the ice/snow mass, rather thanbeing frozen and trapped inside the ice. Accordingly, it is important tocontrol the temperature of the chilled air inside the chamber to obtainoptimum results, as well as to allow enough time for the salt brine torunoff, before the ice mass is removed from the chamber. In some cases,there may be some droplets that will have been deposited during the lastfew seconds of a cycle that will not have had sufficient time to permitthe brine runoff. This is a small fraction that will contribute to thevery small amount of impurities in the final potable water.

The freezing of the seawater preferably enables buoyant pure water iceparticles to be formed, with trace amounts of salty brine adheringthereto, with the objective being to leave behind the salt and otherimpurities in the salty brine, at the bottom of the chamber. Thedesalination system preferably removes the ice particles from the saltybrine, which is denser than the ice particles, so that gravity can helpseparate the brine from the ice particles, and clean the ice particles,in one of at least two ways.

First, the ice particles can form an ice/snow mass, by allowing the iceparticles to accumulate at the bottom of the chamber, i.e., as they fallon top of each other. Over time, as the ice particles fall, and theystick together, they will collectively form an ice mass, which will tendto float on top of the salty brine, where the liquid brine is denserthan the solid ice. In this respect, the system is preferably adapted sothat ice particles will form a conical shape ice mass, by introducingseawater droplets into the center of the chamber, wherein the iceparticles formed thereby will also accumulate in the center of thechamber. The seawater spray is preferably directed toward the centerlineof the chamber, so that the ice particles do not collect on the walls,and so that the ice mass that forms at the bottom of the chamber tendsto form in the center of the chamber, i.e., in the shape of an invertedcone. On one hand, this advantageously enables the salty brine thatencapsulates or adheres to each pure water ice particle to run down thesides, rather than being trapped inside the ice mass i.e., in pockets orcrevices that might otherwise form on the mass as it solidifies. Byforming a cone shaped ice mass, the brine that adheres to each iceparticle will simply run off down the sides, rather than being trapped,so that the salty brine can be effectively separated from the ice massas needed. On the other hand, studies have shown that the ice mass thatforms may form channels and voids throughout so that any accumulatedsalt brine could simply pass through the mass, via the channels andvoids, without being trapped. The ice mass, in this respect, looks morelike snow, and is porous, to allow the brine to pass through.

In addition to ice formation in flight, especially at extremely coldtemperatures, there is another mechanism that creates a porous mass atthe bottom of the crystallization chamber. Consider the ideal case ofhard spherical droplets collecting at the bottom of the chamber. In themost dense packing configuration, the highest density is the ratio ofthe volumes of the sphere compared to the cube of air that surrounds it,or [4/3*pi*r³]/[8r³] or 0.52 gm/cc. It is expected that the true densitywill fall between this ideal value and the density of snow, which is0.10 gm/cc. This provides sufficient porosity for the liquid brine tofind an open passage to the bottom of the collected mass. Once the denseliquid brine starts flowing, the ice particles buoy further apart, andthe brine drains faster.

The embodiment also preferably has means for rinsing the ice mass withfresh water, the fresh water freezing onto the accumulated frozen massof ice/snow and releasing the attached brine layer as more and moredroplets are deposited. For further removal of the brine that attachesitself to the surface of each ice particle, there is preferably aninjection of fresh water on the layer of ice/brine deposited at thebottom of the chamber to assist the gravity drainage of the salty brineon a layer-by-layer basis. This fresh water freezes as it attaches toeach layer and further displaces the very thin viscous salty brine layerfrom the interstices between the ice particles. The fresh water that isfrozen on the ice particles is later thawed and preferably recovered forre-use without the use of additional fresh water. If even higher puritywater is required, a downstream wash column can be added. In thisrespect, additional fresh water at room temperature, such as at 60degrees F., can be sprayed down onto the ice mass to help remove thesalty brine from the ice mass as the mass forms. The majority of thesalt brine is displaced from the spaces between the ice particles bygravity flow. The salty brine is preferably drained out of the bottom ofthe chamber, through a drain.

The bottom section of the chamber preferably comprises a perforatedbasket, which is able to catch the falling ice particles, to form theice mass thereon, but which allows the chilled air to circulate out ofthe chamber. In this respect, the side walls of chamber preferably hasan exit port through which the excess chilled air can flow out of thechamber, wherein the chilled air can then be distributed to the airconditioning system and used as chilled air. Other means (other than theperforated basket) for removing the ice/snow mass, such as pistons, andpincers, are also possible. The ice particles that form at the bottom ofthe basket preferably from a large ice mass, or, in some cases, aslurry, wherein the perforations in the basket allow the salty brine topass through, leaving behind the pure water ice particles in the basket.Then, by removing the basket, the pure water ice mass and/or slurry canbe removed from the chamber.

The mass of ice particles which is removed can then be melted, toproduce fresh water at the bottom of a holding tank. Fresh water atrelatively warm temperatures, in this case, at plus 60 degrees F., canbe sprayed down like a wash column onto the ice particles, to rinse theice, and cause the ice to melt. Alternatively, or in conjunction withthe rinse water, local warm air can be brought into the holding tank, tofurther assist in melting the ice particles. As the ice melts, the freshwater droplets can pass through the perforations in the basket, andcollect at the bottom of the holding tank, in the form of chilled freshdrinking water. More than one basket can be used so that thedesalination and melting processes do not need to be interrupted whileremoving each basket from the chamber. Other means of removing andmelting the ice mass, such as using a drop down door, that allows theice mass to drop onto a conveyor, so that it can be moved to where itcan more easily be melted, can also be provided.

Because the ice mass is made of ice, and therefore, is cold, the freshwater that is produced when it melts will be chilled water. From there,the fresh chilled water can be distributed for drinking purposes, orused for other purposes, such as being stored for later use by the airconditioning system, or re-circulated back to the crystallizationchamber to be used as the spray for the wash column, or spray in theholding tank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing a compressed air energy storagetank version of the desalination system of the present invention,wherein wind power or other energy source is used to co-generate chilledair for desalination purposes.

FIG. 2 is a schematic drawing showing the surge tank version of thecompressed air energy system of the present invention.

FIG. 3 is a schematic drawing showing the tank-less version of thecompressed air energy system of the present invention.

FIGS. 3 a and 3 b are data sheets relating to the secondary compressorand the heat exchangers that are used to keep the chilled air cool.

FIGS. 3 c and 3 d are graphs showing different turbo expanderdischarges.

FIG. 4 a is a flow chart showing a configuration scenario that providesmaximum electricity.

FIG. 4 b is a flow chart showing a configuration scenario that providesa combination of electricity and chilled air.

FIG. 4 c is a flow chart showing a configuration scenario that providesmaximum chilled air and no electricity.

FIG. 5 shows the thermodynamics of a 500 kW turbo expander.

FIG. 6 shows a snow porosity chart showing the density of snow comparedto air temperature.

FIG. 7 shows a standard composition of seawater, including the weightpercent and eutectic temperature for each component.

FIG. 8 shows the requirements for clean drinking water.

FIG. 9 shows temperature regimes for water droplet phases.

FIG. 10 shows characteristics of spray nozzles.

FIG. 11 shows a range of droplet sizes that are possible by nozzle type.

FIG. 12 shows a chart of water droplet temperature and residence time,within a cold air stream (1 k and 2 k micron).

FIG. 13 shows the terminal velocity for water droplets in air.

FIG. 14 shows a section view of the main mixing chamber with pipesand/or cavities extending around the walls thereof for circulatingseawater and/or heated compressed air or water through the chamberwalls.

FIG. 15 shows a section view of the main mixing chamber with chilled airbeing injected from the top of the main chamber, referred to as“co-flow.”

FIG. 16 shows a section view of the main chamber with chilled air beinginjected upward against the falling seawater droplets, referred to as“counter-flow.”

FIG. 17 shows a section view of the main chamber with a counter flowarrangement showing the injection height “H” of the chilled air.

FIG. 18 shows a section view of the main chamber with a counter flowarrangement showing the injection height “H” of the chilled air, and theannulus gap around the conical ice mass.

FIG. 19 shows a possible evolution of the liquid fraction during acooling and warming cycle of a salt solution.

FIG. 20 shows an equilibrium phase diagram for a salt water solution atbelow the eutectic concentration of 23.3%.

FIG. 21 shows a chart of centerline water droplet temperatures with aresidence time of 0.2 seconds (1 k and 4 k micron).

FIG. 22 shows a chart of centerline water droplet temperatures with aresidence time of 2.0 seconds (1 k and 4 k micron).

FIG. 23 shows density variations for water and ice as a function oftemperature.

FIG. 24 shows density variations for saltwater as a function ofpercentage of sodium chloride.

FIG. 25 shows a section view of the main chamber showing a counter flowsystem wherein chilled air is introduced so that it travels upwardinside the chamber against the falling seawater droplets, wherein ahydraulic lift is provided to remove the ice mass when the cycle iscompleted.

FIG. 26 shows a section view of the main chamber showing the counterflow system of FIG. 25 wherein chilled air is introduced so that ittravels upward inside the chamber against the falling seawater droplets,wherein an ice mass begins to form at the bottom of the chamber whereconcentrated salt brine collects.

FIG. 27 shows a section view of the main chamber showing the counterflow system of FIG. 25 wherein chilled air is introduced so that ittravels upward inside the chamber against the falling seawater droplets,wherein an ice mass forms at the bottom of the chamber and concentratedsalt brine collects and solid salt deposits form.

FIG. 28 shows a section view of the main chamber with an embodimenthaving pincers that grab the ice mass after it has formed, and the cyclehas completed.

FIG. 29 shows a section view of the main chamber after completion of thecycle, wherein the remaining cold salt brine at the bottom of thechamber is introduced into a heat exchanger which helps to pre-cool theincoming seawater that is introduced into the chamber.

FIG. 30 shows a section view of the main chamber after completion of thecycle, wherein the remaining solid salt deposits are removed using ahydraulic lift.

FIG. 31 shows a schematic of the desalination system with acrystallization chamber that uses chilled air to freeze particles ofseawater injected into the chamber as a mist or spray, wherein thechilled air is introduced from above, referred to as co-flow.

FIG. 32 is a schematic of the desalination system shown in FIG. 31,showing how the ice particles build up at the bottom of the chamber toform an ice mass, where a perforated basket is used to remove the ice.

FIG. 33 is a schematic of the desalination system shown in FIG. 31,showing how the ice particles can be removed from the chamber, andmelted using a wash column in a holding tank.

FIG. 34 is a schematic of the desalination system shown in FIG. 31,showing how the ice particles can be removed from the chamber, andmelted using local warm air, where a perforated basket is used to removethe ice.

FIG. 35 shows a chart of centerline water droplet temperatures with aresidence time of 2.0 seconds (200 and 4 k micron).

DETAILED DESCRIPTION OF THE INVENTION

The freeze crystallization method of desalinating water discussed aboverequires a cooling system to freeze the seawater which is needed toseparate the pure water from the impurities in the seawater. The presentinvention uniquely incorporates the use of compressed air energytechnology as a means of co-producing chilled air as a by-product,wherein a turbo expander can be used to release and expand compressedair energy, to produce a suitable amount of chilled air for desalinationpurposes.

A. Compressed Air Energy Systems:

The present invention preferably contemplates using one of at leastthree different methods of producing chilled air, including (1) acompressed air energy storage system having a compressor and a largehigh pressure storage tank, wherein a turbo expander is used to releaseand expand the compressed air energy when it is needed, wherein theenergy can be converted into chilled air and/or electrical energy, (2) aturbo expander having the dual capacity to generate electricity andchilled air, wherein the electricity generating capability is preferablyreplaced by a supplemental compressor capability that uses the turboexpander work to replenish the discharged compressed air in anassociated surge tank, and (3) a turbo expander having the capacity toproduce chilled air without having to store the energy first. Each ofthese systems will now be discussed.

1. Compressed Air Energy Storage Tank System:

This embodiment, as shown in FIG. 1, preferably comprises a compressedair energy storage system 1, with an electric motor 3, primarycompressor 7, storage tank 5, a control valve 9, turbo expander 11 andturbo generator 13 for generating electricity. In FIG. 1, “A” designatesthe route whereby electrical energy is transmitted from energy source 2,which can be a wind turbine 4, wind farm, diesel engine, powergenerator, or any conventional source of energy, such as a geothermalpower generation plant, nuclear power plant, fossil fuel powergeneration plant, or the power grid, to electric motor 3. Some of thesepower sources often generate power in excess of power demand. The excesspower would be stored in the form of compressed air. When electric poweris recovered from the compressed air to fill power demand, theco-generated super chilled air would be used for desalination. The motor3 preferably drives the primary compressor 7, to compress air that isthen stored in storage tank 5.

The compressed air energy can preferably be stored in tank 5 for anextended period of time, until the energy is needed. Then, at theappropriate time, the control valve 9 can be used to release thecompressed air so that it can be expanded by turbo expander 11. At thispoint, if desired, and particularly when electrical energy is needed,the waste heat generated by the primary compressor 7 can be circulatedto turbo expander 11, to reduce and offset the effect of super coldtemperatures. However, when chilled air is desired, as would be the casewhenever desalination is desired, it would be beneficial not to use anywaste heat, since heat would simply increase the temperature of thechilled air. At the same time, the waste heat can be used to regulatethe temperature of the chilled air, if precise temperatures are desired.

One of the outputs that can be produced by this system 1 is in the formof electricity, which can be generated directly by turbo generator 13,as the compressed air is released from tank 5 by turbo expander 11, tocreate a high velocity air flow. Another output that is produced is inthe form of chilled air, which is co-produced as a by-product as thecompressed air from tank 5 is released and expanded by turbo expander11. In either case, the present system 1 is preferably adapted so thatthese outputs can be generated at the same time, i.e., the compressedair can generate 1) electricity using turbo generator 13, 2) chilled airusing turbo expander 11, or 3) both electricity and chilled air, asdictated by the needs of the system.

High-pressure storage tank 5 is preferably provided and designed towithstand the high pressures likely to be generated by primarycompressor 7, and insulated to maintain a consistent temperature in thetank. Tank 5 can also be in the form of a pipeline or other containerfor holding pressurized air, as described in more detail in U.S.application Ser. No. 11/585,023, filed on Oct. 23, 2006, which isincorporated herein by reference. The term “tank” will be used toinclude pipes and other compressed air storage mediums, and in thisrespect, the pipeline discussed in Applicants' U.S. provisionalapplication Nos. 60/763,577, filed January. 31, 2006, and 60/834,232,filed Jul. 28, 2006, as well as U.S. non-provisional application Ser.No. 11/407,733, filed Apr. 20, 2006, which are incorporated herein byreference, can be used. Tank 5 is also preferably located in proximityto compressor 7, and turbo expander 11, such that compressed air can beconveyed to tank 5, and then circulated to turbo expander 11, withoutsignificant pressure loss. Although the present invention contemplatesthat various size tanks can be used, the present system preferablycontemplates that the size of the tank should be based on the needs ofthe system, the size of the facility or demand, the cost of the system,etc., as necessary to provide a sufficient amount of compressed airenergy for storage. When there is insufficient room for a tank, or whena specific application is considered, the surge tank or tank-lessversions, to be discussed, can be used.

The present invention contemplates that any conventional means ofreleasing air and converting the compressed air into electrical energyand/or chilled air can be used. In the preferred embodiment, one or moreturbo expanders 11 are used to release the compressed air and create ahigh velocity airflow that can be used to power a turbo generator 13 tocreate electrical energy. This electricity can then be used tosupplement the electrical energy supplied directly by the energy source,as needed, or to drive a supplemental compressor, which can produceadditional compressed air that can be recycled and stored in tank 5. Inthese embodiments, turbo expander 11 preferably feeds energy to analternator, which is connected to an AC to DC converter, followed by aDC to AC inverter and then followed by a power conditioner to matchimpedances to the user circuits. This chain of devices assures that thevariable frequency inputs result in the required constant frequencyoutput.

Optionally, when desalination is not required, one or more means forproviding heat to the compressed air energy system 1 can be provided toboost the generation of electricity by turbo generator 13. The presentinvention contemplates that at least three different types of heatingsystems can be used as a means of providing heat, including 1) solarthermal collectors to utilize energy from the sun, 2) waste heatcollectors to circulate the waste heat generated by the compressors, and3) a separate heating unit, such as a fossil fuel burner, to introduceheat to the system. In this system, because it is normally desirable togenerate chilled air as a by-product for cooling or desalinationpurposes, the waste heat and other heating systems are generally usedonly when electricity is being generated by turbo generator 13, and,when little or no chilled air is needed or being utilized for cooling ordesalination purposes.

The present invention preferably takes advantage of the chilled airbeing generated by turbo expander 11, for additional secondary purposes,such as water desalination and air conditioning, which increases theefficiency of the system. For example, in addition to using the chilledair for purposes of producing direct cooling for air conditioners,and/or rerouted through pipes to the compressors, to keep thecompressors cool, in the preferred embodiment, the chilled air is usedto provide cooling for a desalination system. The exit chilled air fromdesalination can also be used for air conditioning systems and the like.

Logic circuit 6 preferably comprises a control system to control theoperation of storage tank 5, compressor 7, turbo expander 11, turbogenerator 13, heating units, refrigeration components, etc. One primaryfunction of the control system is to direct the power immediately to thecustomer and bypass the compressor, if desired. In such case, only whenthere is excess power available from the power source that the customercannot use is the power sent to the compressor. On the other hand, whenthere is no power available from the power plant, but the customer needspower, the compressed air can be released to supply the required powerdeficit. In those circumstances where there is a deficit in requiredpower, and the storage tank is below the required minimum power, it maybe necessary to turn on the emergency power. The control system ispreferably designed to be able to maintain the level of compressed airenergy in tank 5 at an appropriate level, by regulating the flow ofcompressed air into and out of tank 5. The control system preferably hasa microprocessor that is pre-programmed so that the system can be runautomatically.

A typical 500 kilowatt turbo expander 11 or other conventional expandercan be used in connection with storage tank 5 that stores compressed airproduced by compressor 7. The exhaust air associated with the workperformed by the expansion of the compressed air in tank 5 can generateextremely cold air, which is then used for desalination purposes. Inthis example, the turbo expander 11 preferably enables an input ofcompressed air at a pressure of about 200-psia and 70 degrees F. (inputentropy=1.4552 BTU/#−° R) and an output pressure of 14.67-psia whichwill isentropically expand to about minus 210 degrees F. (outputentropy=1.4552 BTU/#−° R). If the thermodynamic efficiency of theexpansion is only 79% because of the excessively large pressure dropacross the turbo expander, the discharge temperature will be about minus152.7 degrees F.

Similarly, a 500 kilowatt turbo expander with a compressed-air inputpressure of 200-psia and 70 degrees F. (input entropy=1.4552 BTU/#−° R)and an output at a higher pressure of 30-psia will isentropically expandto minus 153.2 degrees F. (output entropy=1.4552 BTU/#−° R). If thethermodynamic efficiency of the expansion over a smaller pressure ratiois 85%, the discharge temperature will be about minus 120.6 degrees F.

In either case, consideration was given to the thermodynamics of thestorage tank and its effect on the air temperature. The air pressurewithin the storage tank will drop as air is being withdrawn from thestorage tank. The air temperature within the storage tank would beexpected to drop near-adiabatically to temperature levels that are notacceptable as input for the efficient operation of the turbo expander.However, the storage tank, because of its thick steel wall needed toaccommodate the high air pressure, also acts as a thermal storage,wherein the steel tank walls retain sufficient heat, even at an initialtemperature of 70 degrees F., to keep the residual air temperaturewithin the tank from dropping significantly. Thus, as the airtemperature within the tank starts to drop, the sensible heat within thetank walls begins to flow in the direction of the negative temperaturegradient between the steel wall and the inside air. The net result isthat the residual air within the tank shows only a moderate temperaturedrop that is acceptable by the turbo expander.

The thermodynamic power of 510 kW (thermal) will likely produce 450 kW(electric) because of the 2% gear friction loss and 10% energy lossduring conversion by the electric generator. The thermodynamics of a 500kW turbo expander is shown in FIG. 5.

In either case, it can be seen that the exhaust air from the turboexpander 11 exhibits extremely low temperatures suitable fordesalination purposes. Such low temperatures, having very highcooling/freezing potential, can be very useful for seawaterdesalination, when using a modified form of the Eutectic FreezeCrystallization (EFC) method discussed below.

2. Surge Tank Compressed Air Energy System:

Another compressed air energy system is shown in FIG. 2. FIG. 2 showsdetails of a compressor 15 and turbo expander 17 of an embodiment inwhich there is only a small surge tank 19, rather than a large storagetank. In this system, energy from the source can be used to drivecompressor 15, wherein the compressed air is channeled into surge tank19, and a control valve 21 is provided to control the extent to whichthe compressed air is released to turbo expander 17. As can be seen inFIG. 2, preferably, the pressurized and expanded output air from theturbo expander 17 is channeled in two different ways. First, theco-produced chilled air from the turbo expander 17 can be channeledthrough a pipe 20 and then distributed to the desalination system, aswill be discussed, or other cooling function. Second, additional energyfrom the turbo expander 17 can be cycled back, via a shaft 18, to a gearbox 16, which in turn, enables a multi stage reciprocating compressor 23to produce additional compressed air energy, which can be cycled backinto surge tank 19, to replenish the discharged compressed air therein.This way, any extra energy produced by turbo expander 17, which is notused in the form of chilled air, can be cycled back to produce morecompressed air, which in turn, can be used to produce more chilled airand/or electricity.

The local atmospheric air is preferably compressed by the reciprocatingcompressor 23 at a flow rate consistent with the backpressure of thestored air in surge tank 19. There is therefore preferably a positiveinflow of air from the first compressor 15 that combines with thepositive inflow of air from the reciprocating compressor 23 that matchesthe negative outflow of air feeding turbo expander 17. This balancehappens at an equilibrium pressure that is dependent upon the SCFM/HPcurves for the compressors 15, 23 and turbo expander 17. The pressurefor a particular set of commercial hardware might be slightly above200-psig.

Note that if it is desired to co-produce electricity with this system,gearbox 16 can be configured so that the rotating shaft 18 of turboexpander 17 can be connected to an electric generator to produceelectricity, and disconnected from the reciprocating compressor 23. Thisoption allows shaft 18 to be connected and disconnected from theimpeller-driven reciprocating compressor 23 which can be used to recyclecompressed air into surge tank 19.

3. Tank-Less Compressed Air Energy System:

FIG. 3 shows details of a “tank-less” compressed air energy system,including compressor 31 and turbo expander 33 of an embodiment in whichthere is no need for a storage tank. In this system, energy from thesource can be used to compress air using electric motor 32, secondarycompressor 34, and turbo compressor 31, wherein the compressed air canbe released using turbo expander 33, without having to store the energyfirst. Electric motor 32 can be driven directly by the electricitygenerated by energy source 3. Compressed air can also be generated bythe energy source 3 directly and routed to drive turbo compressor 31 ifdesired.

As can be seen in FIG. 3, electric motor 32 is preferably used to drivethe secondary compressor 34, wherein the pressurized output air from thesecondary compressor 34 is cooled by a heat exchanger 35, extended alongline 36, wherein the air from compressor 34 is then passed along toturbo compressor 31. The turbo compressor 31 preferably shares shaft 39with turbo expander 33, such that driving one will also drive the other,wherein the system can reach a steady state operation, as will bediscussed.

A second heat exchanger 37 is preferably provided along line 38 betweenturbo compressor 31 and turbo expander 33, such that as the compressedair travels from turbo compressor 31 to turbo expander 33, it passesthrough the second heat exchanger 37, to cool the air once again. Thisway, the air that enters into turbo expander 33 is relatively cold. Asmall surge tank, like the one shown in FIG. 2, may be provided betweensecond heat exchanger 37 and turbo expander 33, if desired. The heatexchange systems used can be incorporated into the mixing chamber walls,as pipes and/or cavities, as will be discussed.

Because turbo compressor 31 and turbo expander 33 are driven by the sameshaft 39, operating one will operate the other, which helps to reducethe overall cost of driving the mechanisms. Indeed, because the electricmotor 32 is able to compress air initially, to create pressure insidethe system, and the pressurized air is channeled into compressor 31, andthen, to turbo expander 33, the force of driving turbo expander 33 canbe used to initially drive compressor 31, thereby eliminating the needto use additional energy to drive either mechanism.

For example, when the initial pressurized-air from the secondarycompressor 34 is passed from turbo compressor 31 to turbo expander 33,the turbo expander 33 starts to rotate, which in turn, causes turbocompressor 31 on the common shaft 39 to rotate as well. Then, as theturbo compressor 31 accelerates in rotational speed, it furtherpressurizes the input air from the secondary compressor 34 into turboexpander 33, causing the turbo expander 33 to accelerate further. Thecycle of accelerating the turbo expander 33 and turbo compressor 31systems with the same shaft 39, using the energy from secondarycompressor 34, can then eventually reach a steady state, wherein theflow through secondary compressor 34, turbo compressor 31 and turboexpander 33 match. The rotational power across turbo compressor 31 andturbo expander 33 can match as well. Compressed air generated by theenergy source can also be fed directly to turbo compressor 31, toachieve the same effect as using secondary compressor 34. Controls areused to control and operate the heat exchangers that are used to helpcontrol the temperatures of the air passing through turbo expander 33.The controls determine which heat exchangers are to be used at any giventime, and how much effect they should provide.

FIG. 3 a shows the following: First, it shows the thermodynamicdescription of the secondary compressor 34 (identified as reciprocatingcompressor) during its operation between 14.67-psia and 90-psia. Thecompression process is considered isentropic so that one can take airfrom 14.67-psia and 70 degrees F., to 90-psia and 426.44 degrees F.(Entropy=1.6366 BTU/(# R). However, it should be noted that thecompression process may be as low as 84% or less efficient, wherein theresult is that more energy is expended to achieve 90-psia, so that thefinal temperature is actually higher, i.e., could be 492 degrees F. orhigher. Water-cooling of the compressor and water-cooling in thedownstream heat exchanger 35 preferably bring the output temperature toabout 70 degrees F. The heated water can then be sent to the hot watersystem as waste heat recovery, if desired, or to the crystallizationchamber walls, as will be discussed. Also consider that there may be apressure drop, such as about a loss of 5-psi, between the secondarycompressor 34 and turbo compressor 31.

A similar process is preferably repeated with the turbo compressor 31(identified as centrifugal compressor) with its 84% efficiency. Theresult is that the 85-psia and 70 degrees F. air is compressed to about205-psia and 250 degrees F., by using about 43.36 BTU/# of flowing air.Again, water-cooling of the turbo compressor 31 and water-cooling in thedownstream heat exchanger 37 preferably bring the output temperature toabout 70 degrees F. The heated water can then be sent to the hot watersystem as waste heat recovery, if desired, or to the crystallizationchamber walls, as will be discussed. Also consider that there is about a5-psi pressure drop between the turbo compressor 31 and turbo expander33. The turbo expander 33 accepts input air at 200-psia and 70 degreesF., and can exhaust chilled air at about 31.5 psia and minus 114.8degrees F. This releases 43.416 BTU/# of flowing air, slightly more thanthe 43.36 BTU/# of flowing air required by the turbo compressor 31.

A sample case is given in FIG. 3 b, wherein a 2,000 hp system canprovide 10,857.6 SCFM air at minus 114.78 degrees F. for chillingpurposes. Note that this was achieved by powering only the 2,000 HPreciprocating secondary compressor 34 at an efficiency of 102.79 BTU/#or 5.5 SCFM/HP. In FIG. 3 a there is 2,000 hp electrical input and 844.3hp thermal output. This represents 42.2% efficiency.

These numbers and amounts are estimated, and are provided for exemplarypurposes only. In actual use, the desalination system of the presentinvention preferably operates with chilled air in the temperature rangeof minus 135 degrees F. to minus 175 degrees F., and therefore, systemshaving greater cooling potential, such as by increasing the amount ofpressure that is released, is contemplated by the present invention.Actual numbers and amounts may vary.

The chill temperature available from the turbo expander can begeneralized by considering an example of a 200-psia input pressure andtwo discharge pressures (1) 30-psia for a one stage turbo expander, and(2) 14.67-psia for a two stage turbo expander. In the first case, the30-psia discharge pressure considers a downstream process wherein thechilled air will need sufficient pressurization to pass through longlengths of piping and valves and their associated pressure losses. Thesecond case, the 14.67-psia discharge pressure considers that there isno downstream plumbing of any consequence and gives the greatestpressure drop (temperature drop) across the turbo expander.

FIG. 3 c shows the strong difference between the airflow requirements toproduce a unit of power (SCFM/hp) for the above two specific cases. FIG.3 c shows that the higher the input temperature, the less airflow isrequired to produce a unit of power. So, higher input temperatures willrequire less compressed air energy, including a smaller storage tank, toproduce a given amount of power for the same power discharge time. Onthe other hand, FIG. 3 d shows that the lower input temperature willproduce a lower discharge temperature. Furthermore, FIG. 3 d shows thatdischarging from 200-psia to 14.67-psia (atmospheric pressure) producesextremely low temperatures for lower input temperatures. Thus if thegoal is desalination, or air conditioning, it is necessary to considerthe larger pressure drop and colder input temperatures.

B. Applications of Present Desalination System:

The present desalination system can be used in virtually any applicationwhere the need for desalination exists. For example, there may be a needto supply fresh water to a town located near a seashore site that is ina drought season, or there may be plentiful brackish well wateravailable in a desert. In the following section, two unique applicationswill be considered: (1) Shipboard application, and (2) Island or onshoreapplication. In the shipboard application, the objective is to maximizethe production of fresh water at the sacrifice of electric power (seeFIG. 4 c, which shows Scenario #3). Whatever electric power is producedwill be cycled back to operate the air compressor, such as by using thesurge tank compressed air energy system described above. In the islandapplication, flexibility is desired to be able to switch from onescenario to another, either maximizing electric power, maximizingdesalination, or maintaining a balance of both (see FIGS. 4 a, 4 b and 4c, which show Scenarios #1, #2 and #3).

1. Shipboard Application:

As seen in Scenario #3, in FIG. 4 c, diesel fuel available on board aship can be used to operate Compressor #1, 55. Compressor 55 preferablyfeeds compressed air into a very small surge tank 57. Surge tank 57 hasone exit that feeds into the turbo expander 61 which, in turn, expelsextremely cold air. The shaft of turbo expander 61 is preferablyattached to a turbo compressor wheel, Compressor #2, 59, that takeslocal atmospheric air and compresses it so that it can feed compressedair back into surge tank 57. Thus the net system uses diesel fuel todrive Compressor #1, 55, and then super chilled air is the by-product.As will be discussed, this super chilled air can interact with seawaterand generate pure water using the desalinating system described herein.This device can be made relatively small and can generate a significantamount of freshwater when compared to other existing systems that areused on ships, such as the reverse osmosis method.

In a variation of this embodiment, the on-board ship system can also bedriven by a wind turbine 51 mounted on the ship, to use wind generatedenergy to drive compressor 55. Wind turbine 51 can be mounted so that itcan swivel and at any time be aimed toward the wind, such that the wind,either in combination with, or instead of the power of the engine on theship, can be used to generate energy to drive the compressor. Compressor55 is preferably gear driven such that energy from the wind turbine isused directly without being converted into electricity first, whichincreases efficiency.

2. Island and Off-Shore Application:

The Island Application preferably uses any of the compressed air energymethods described above to co-generate electricity and/or chilled air.First of all, during the period of time when only electricity is needed,a heater or waste heat can be used to preheat the input compressed airto the turbo expander 61 (to about 350 degrees F.) to optimize thegeneration of electricity, with reduced consumption of compressed air,and essentially no chilled air from the turbo expander. However, duringthe period of time when both electricity and chilled air (fordesalination and air conditioning purposes) are needed, the heat inputis preferably turned off. In such case, the turbo expander generateselectricity with increased consumption of compressed air, and chilledair is expelled from the turbo expander as a by-product to feed thedesalination and/or cooling system. The cold air that passes through thedesalination system can also be used to provide cooling for an airconditioner.

During the period of time when (a) no electricity is needed, and (b)chilled air is needed for desalination and/or air conditioning purposes,the heater input is preferably turned off. Preferably, the surge tank“cycle back” system described above can be implemented. In such case,the turbo expander 61 preferably generates reduced electric power, ornone at all, and chilled air is expelled from turbo expander 61 to thedesalinating system and/or cooling system. And, whatever electric poweris produced is cycled back to operate the reciprocating compressor #2,59. In this mode of operation, the volume of the surge tank is notrelevant. A steady pressure is reached in tank 57 such that a giveninput compressor power puts out a fixed flow of chilled air. Compressors#1 and #2 preferably operate continuously.

3. System Scenarios:

In Scenario #1, shown in FIG. 4 a, there is interest in generating themaximum level of electrical power while exhausting the storage tank 57at the minimum flow rate. This can be accomplished by using waste heatfrom nearby equipment (or solar irradiation) or compressor 55 to heatthe pressurized air fed to turbo expander 61. The higher initialtemperature, say, about 300 degrees F., will produce an exhaust airtemperature from the turbo expander 61 that is slightly below roomtemperature. Thus, although electricity is produced, there is no usefulco-generated chilled air. The turbo expander 61 impeller material shouldbe titanium at the high tip speeds of the rotating impeller.

In Scenario #2, shown in FIG. 4 b, there is interest in producingelectrical power and simultaneously producing exhaust chilled air fromturbo expander 61 that is extremely cold. Thus, there is co-generatedchilled air that can be used for air conditioning systems,refrigerators, food lockers and, in the preferred embodiment,desalination systems. The turbo expander 61 can operate at temperaturesbelow 70 degrees F. so that it is acceptable for impeller material to bemade of high strength aluminum at the high tip speeds of the rotatingimpeller.

In Scenario #3, shown in FIG. 4 c, there is no interest in producingelectrical power, but there is interest in producing chilled air fromturbo expander 61. Thus there is co-generated chilled air that can beused for air conditioning systems, food lockers, refrigerators, and inthe preferred embodiment, desalination systems. The turbo expander canoperate at temperatures below 70 degrees F. so that it is acceptable forimpeller material to be made of high strength aluminum at the high tipspeeds of the rotating impeller.

C. Eutectic Freeze Process:

An existing technology called the Eutectic Freeze Crystallization methodhas attracted attention in recent years. In the context of desalinatingseawater containing salt, the eutectic freeze crystallization processtakes advantage of the freezing process, and the phase diagram ofsaltwater solution, as shown in FIG. 20.

Pure water will begin to freeze at 0 degrees C. (32 degrees F.),whereas, a solution of saltwater containing 3.5% salt concentration willbegin to freeze at about minus 1.9 degrees C., wherein the ice thatforms is essentially salt free, with a density of about equal to that offreshwater ice. The lowest temperature at which a saltwater solutionwill remain a liquid is minus 21.1 degrees C. or about minus 6.2 degreesF. The fresh water components of the saltwater solution begin to freezeprior to reaching that temperature, by forming ice crystals, but at thattemperature, not only has the fresh water frozen, but the salt solutionbegins to crystallize out of solution as pure NaCl crystals and hydratedNaCl*2H₂O), along with the ice, until the liquid in the solutioncompletely freezes to a solid. The frozen solution is a mixture ofseparate of NaCl crystals and hydrated NaCl*2H2O crystals as well as theoriginal frozen fresh water ice crystals. This boundary between thewarmer two-phase mixture and colder one-phase heterogeneous mixture iscalled a eutectic mixture.

The point at which a eutectic mixture is in equilibrium with thesolution makes a wonderful calibration point for a temperature scalewhen there is only one salt solute in the water. Each solute has its owneutectic temperature and concentration. This is because a mixture oftwo-phases (ice fresh water ice and saltwater) and one solid phase isstable at one temperature and at one temperature only per eachparticular solute. If there is a transition from two-phases to one phasesolid, the temperature must be at minus 21.1 degrees C. (or minus 6.2degree F.).

The sequence of steps in the Eutectic Freeze Crystallization process canbe explained based on a typical water-salt phase diagram, as shown inFIG. 20. If a saltwater solution is cooled below the freezingtemperature designated by the liquidus boundary line, ice crystals willstart to form. This line is at an angle to show that the freezingtemperature of the saltwater solution is dependent on the level of saltconcentration therein. For example, when there is 0 percent saltconcentrate, the freezing temperature is 32 degrees F. However, when thesalt concentration level increases, by moving down along the liquidusboundary line, the temperature at which the ice crystals will formdecreases. For example, when there is a 10 percent salt concentration inthe solution, the freezing temperature becomes lower, i.e., somethinglike 15 to 20 degrees F. Then, with continued cooling, and as more iceis formed, the saltwater solution becomes more concentrated with salt.Therefore, its composition moves along the liquidus boundary line andeventually reaches a point called the eutectic point, wherein thesolution is saturated with salt (with a salt concentration of 23.3%). Atthis concentration, ice crystals will form when the temperature is atthe eutectic temperature of about minus 6.2 degrees F. Further coolingbelow minus 6.2 degrees F. will result in the formation of a mixture ofthree solids: 1) solid pure water ice crystals, 2) solid pure saltcrystals, and 3) solid pure hydrated salt crystals in a single solidphase that does not permit separation. The eutectic point of NaCl is atminus 6.2 degrees F., and the eutectic composition is 23.3%.

In the present invention, the ice mass preferably operates at atemperature slightly above this temperature, in order to avoidcrystallization of salt. Thus, only the area above the solidus boundary(below 23% salt concentration), which represents the region of the phasediagram above EFC temperature, are preferably used. The extreme far leftregion of the phase diagram (0% salt) represents pure ice/snowformation, and the central region represents the salty brine. Theextreme far right region of the phase diagram and the region below thesolidus boundary include pure solid ice crystals, pure solid “salt andhydrated water” crystals and pure solid salt crystals in a single solidphase that does not permit separation and are not used in the presentsystem.

The NMR tests performed by Dr. Herman Cho of Pacific NorthwestLaboratories showed that when a salt solution is frozen to below theeutectic temperature, it returns “immediately” to its two phasecondition when thawed to warmer than the eutectic temperature. This isan important data point for describing the behavior of the very smalldroplets in the crystallization chamber.

It should also be considered that standard seawater from the oceancontains additional minerals and impurities other than salt, as shown inFIG. 7. FIG. 7 shows the standard composition of seawater. For eachcomponent the weight percent and the eutectic temperature are given. Onthe other hand, FIG. 8 represents the requirements for clean drinkingwater. Usually 3% salt concentration in the seawater, when brought to0.03% salt concentration, is considered potable. Fresh water isconsidered to be any salt concentration below 0.05%, whereas, the termbrackish water is commonly given to water having a salt concentration ofbetween 0.05% and 3.0%. The term saline water is commonly given to waterhaving a salt concentration of between 3.0% and 5.0%, and the term brineis commonly given to water having a salt concentration of more than5.0%. Again, the term “seawater” will be used throughout to refer to anywater needing to be purified, whether from the sea or not.

Note that by using the eutectic temperature of minus 21.2 degrees C. (orminus 6.2 degrees F.) to extract sodium chloride (NaCl), thecrystallization process will leave the following minerals: CalciumChloride (1.36 g/liter of intake) and Magnesium Chloride (4.66 g/literof intake). These are two products that can be salvaged for furthereconomic benefit. If there is interest in further removing otherminerals, such as potassium chloride, magnesium sulfate and sodiumbicarbonate, more careful control of the slush temperature can assurethat these compounds do not get frozen into the ice and instead willremain in the brine solution for later recovery in additionalprocessing. When fresh drinking water is the end goal, the presentinvention contemplates using filters to remove as many impurities fromthe seawater as possible before it is used in the desalinationprocesses. The invention contemplates using any of the other mineralsfor further economic benefit.

Very little information has been published on the EFC method, presumablydue to the alleged complexity of EFC compared to its competitiveconventional techniques, such as evaporative and coolingcrystallization. With the ongoing advancements in wash column technologyand the large scale application of melt crystallization as an ultrapurification technique, the most forwarded disadvantages of EFCconcerning investment costs and scale limitations can be overcome, andtime has come to consider its commercial application.

As discussed above, the EFC process of the present invention isdifferent from other processes, in that it involves the formation ofpure water ice crystals that can be separated from the impurities thatare in the base water. It is important for the droplets to freeze toform a two-phase solution of solid ice particles and liquid brine, so itis desirable for the droplets to reach at or near the eutectictemperature while in flight. On the other hand, if the droplets becometoo cold (colder than the eutectic temperature) as they fall through thechamber, the fresh water within each droplet could freeze together withthe solid salt crystals and solid brine, in which case, it may not bepossible to separate the salt from the fresh water.

This can happen, for example, when the seawater spray consists of varieddroplet sizes, wherein the smaller droplets may reach below the eutectictemperature and completely freeze by the time they reach the bottom ofthe chamber. In this respect, consider that the spray nozzle that isdesigned to disperse a cloud of mean size close to 4,000 microns indiameter will also generate a smaller fraction of mass flow but a hugenumber of droplets in the range of 400 microns in diameter. Thesesmaller particles have a ten-fold smaller settling velocity and willhave a ten-fold longer residence time. Furthermore, these smallerparticles will freeze faster and to temperatures far below the eutectictemperatures when they interact with the minus 135 deg F. or minus 175deg F. local air stream exiting the nozzles in the co-flowconfiguration. Even though typical nozzles spray larger diameterparticles, there will always be smaller particles, including adistribution of particle sizes within a certain range. The smallerparticles are likely to be large in numbers, but will not contribute toa very large mass overall.

Therefore, the small droplets in downward flight through this extremelycold temperature regime will indeed cause undesirable crystallization ofthe droplet into one solid particle composed of (1) Solid ice of freshwater, (2) Solid salt with each salt molecule bound to two watermolecules with attached water molecules, and (3) Solid salt crystals.During the flight of the small particle in the cold air there is noseparation of the brine from the fresh water. However, as will bediscussed, the separation will occur when the droplet deposits on themass of accumulated ice particles created from the large droplets at thebottom of the chamber, which preferably has an equilibrium temperaturethat is warmer than the eutectic temperature.

The very small particle on the order of a few hundred microns indiameter may freeze completely through to their centers when exposed toair temperatures far colder than the eutectic temperature, in the regimeclose to the spray nozzle. When these small droplets deposit on thewarmer ice/snow mass at the bottom of the crystallization chamber, theyare preferably warmed to about the equilibrium temperature of slightlywarmer than the eutectic point. Thus if the small droplets undergofreezing to below the eutectic temperature, they can thaw back up toabove the eutectic temperature. At that point, the usual separation ofthe solid porous snow/ice structure and the liquid salt solution (brine)will occur. In the invented process, therefore, at least at the bottomof the chamber, the crystallization temperature is preferably maintainedat a level slightly above the eutectic freeze crystallizationtemperature in order to avoid salt crystallization. The net result isthe formation of pure ice/snow and residual liquid brine.

The operation of the crystallization chamber at the eutectic temperatureresults in the highest possible conversion of seawater to sweet water,85.7%. However, the porosity of the ice/snow mass may be higher atslightly warmer temperatures so that less than 85.7% conversionefficiency is sacrificed to obtain a higher purity of the final freshwater.

The present invention represents a novel variation of the EFC system,wherein clean chilled air is used as the refrigerant, and is mixed witha seawater droplet cloud, to cause the seawater to reach near theeutectic point, so that pure water ice crystals can be formed, which canbe removed from the salty brine solution remaining after the icefreezes. In the present invention, it is intended that the systemoperate mostly above the eutectic point, particularly when the icecrystals begin to settle, so that the formation of solid salt crystalscan be avoided.

One of the goals of the present invention is to ensure that the seawateris adequately frozen by exposure to the chilled air introduced andintermixed with the seawater in a mixing chamber. To do this, thepresent invention contemplates introducing extremely cold air into themixing chamber, such as air chilled to preferably between minus 135degrees F. to minus 175 degrees F., and then pressurizing the seawaterand injecting it into the mixing chamber through nozzles in the form oftiny seawater droplets, which can more easily be mixed, cooled andaffected by the chilled air. And, to ensure that adequate freezing andseparation can occur, it is significant to determine the size, velocityand pressure of the droplets and how they are formed and introduced intothe chilled air flow, as well as the temperature, volume flow rate andrelative direction of the chilled air, as well as the size of the mixingchamber.

FIG. 9 shows the temperature regimes for the various phases of a waterdroplet. The Bergeron Process, named after its discoverer, Tor Bergeron,involves supercooled water droplets. The term supercooled refers towater that is still a liquid at temperatures below the freezing point of0 degrees Celsius or 32 degrees Fahrenheit. Studies have shown thatwater in very small drops, such as the size of a cloud droplet, canexist at temperatures well below freezing (as low as minus 40 degrees C.or minus 40 degrees F.).

The present invention preferably utilizes a mixing chamber, such asthose shown in FIGS. 14-18 and 25-31, for mixing the chilled air withthe seawater droplets. The mixing chamber is essentially a containerpreferably having insulated walls in which the seawater droplets andchilled air can be introduced and intermixed until they collectivelyreach near (slightly above) the Eutectic Temperature, which, asindicated above, for saltwater, is minus 21.1 degrees C. The size andconfiguration of the chamber can vary, depending on the needs, andcapacities that are desired, as will be discussed.

To help ensure that proper mixing occurs, the seawater is preferablypressurized and passed through one or more nozzles to form a spray,which forms a seawater droplet cloud, or mist, that is preferablyintroduced into the chamber. Any of various nozzle configurations arepossible, depending on the desired results to be achieved.

Full cone nozzles form complete spray coverage in a round, oval orsquare shaped area. Usually the liquid is swirled within the nozzle andmixed with non-spinning liquid that bypasses an internal vane. Liquidthen exits through an orifice forming a conical pattern. Spray angle andliquid distribution within the cone pattern depend on the vane designand location relative to the exit orifice. The exit orifice design andthe relative geometric proportions also affect the spray angle anddistribution. Full cone nozzles provide a uniform spray distribution ofmedium to large size droplets resulting from their vane design whichfeatures large flow passages and control characteristics.

FIG. 10 shows several characteristics of spray nozzles. The full-coneconfiguration may be most applicable to the present application. Withineach type of spray pattern, the smallest capacities where the capacitiesare defined by the lowest pressure drop across the orifice where theorifice diameter is small, will produce the smallest spray drops. Thelargest capacities produce the largest spray drops. Although with mostnozzles, a range of different size droplets (distribution) willinevitably be formed. For example, a nozzle with VMD of 4,000 micronsdiameter will have the largest mass flow of droplets at 4,000 microns.However, there will also be a much smaller mass flow of particles at thesmaller size of 400 microns in diameter. Volume Median Diameter (VMD) isbased on the volume of liquid sprayed; therefore, it is a widelyaccepted measure. FIG. 11 shows the range of drop sizes possible bynozzle type.

Note that in one embodiment of the present invention, there would bemixing between the input seawater and the chilled air, wherein about 250pounds per minute (250 #/min) of seawater could be processed with apredetermined amount of chilled air, which has been calculated to beabout 7,151 standard cubic feet per minute (7,151 SCFM). In such case,there would ideally be about 214 #/min of ice (fresh water) recovered.Based upon a turbo expander efficiency of 9.9 SCFM/hp and a compressorefficiency of 2.2 SCFM/hp, there is 7.1 kW input electrical power togenerate a pound per minute of fresh water.

In order to transfer 11,000 pounds of saltwater in 120 minutes, thespray nozzle that is selected must pass a minimum of 10.76 gallons perminute. Thus the full cone nozzle having a capacity of 12 gallons perminute and 4,300 microns VMD could be applied to that sample embodiment.Note that heavy rainfall consists of particles with VMD of 2,000 to5,000 microns. Droplets over 8,000 microns in diameter break up intofragments when reacted with a relative wind. In this example, the volumeflow rate can dictate the design of the equipment, including the size ofthe nozzles, and operating pressure thereof, and therefore, the size ofthe seawater droplets, in cases where a desired rate of fresh waterproduction is necessary. In other examples, the size of the nozzles andthe seawater droplet sizes can be determined based on the optimumcharacteristics that are sought to be achieved, for the maximumefficiency of the equipment in the production of fresh water.

The size of the seawater droplet is preferably controlled, as much aspossible, and predetermined, to ensure that proper mixing and adequateheat transfer occurs, to help ensure that proper freezing takes place.Preferably, the droplets will need only a very short amount of time tocompletely freeze, from the outer surface of the droplet, to the core ofthe droplet, an example of which can be seen in FIG. 12. This can be afunction of the droplet size, as well as the temperature, and volumeflow rate and direction of the chilled air, which is also a function ofthe size of the chamber, and how long the droplets are exposed tochilled air, i.e., residence time. The droplets must be small enough tobe quickly frozen, but large enough so that they eventually fall to thebottom of the chamber, notwithstanding the flow rate of the chilled air.

Generally speaking, the droplet size can be affected by the amount ofpressure that is used to force the seawater through the nozzles. Whenmore pressure is used, the droplet diameter will tend to be smaller, andwhen less pressure is used, the droplet diameter will tend to be larger.For example, when a pressure of about 28 psia is used, the droplets willtend to be relatively small, resulting in a downward velocity of about26 feet per second, into 14.67 psia atmosphere. On the other hand, atlower pressure, say, about 16 psia, the droplets will tend to be larger,resulting in a downward velocity of about 8.3 feet per second, into a14.67 psia atmosphere. Nevertheless, with most nozzles, it is not alwayspossible to completely control the size of each seawater droplet that isformed, so the present invention must take into account the possibilitythat a range of droplet sizes will be formed when the spray is made.However, the nozzles are designed for a specific nominal droplet size.Statistically, the nominal droplet size will be the median (VMD) value,with a typical bell-shaped distribution. For quality manufacturednozzles, the normal distribution will be relatively narrow and highlypeaked so that the majority of particle sizes will be near the medianvalue. The outer size region above and below the mean would not have asignificant effect of the desalination system performance.

Another consideration is the flow rate of the chilled air in thechamber. In conjunction with the droplet size, how long a droplet willbe exposed to and suspended within the chilled air, and how it willcirculate within the mixing chamber, will depend on the relativevelocities of the droplets and chilled air. That is, the velocity atwhich the droplets fall to the bottom of the chamber can be varied byadjusting the direction and flow rate of the chilled air in the chamber,as will be discussed. In this respect, the relative direction of theseawater spray and chilled air being introduced into the chamber cancontribute to the proper formation of the ice crystals. In this respect,the present invention contemplates both a 1) counter-flow and 2) co-flowarrangement.

D. Counter-Flow:

To achieve a counter flow arrangement, the chilled air and seawaterspray are introduced into the chamber in opposite directions. This canbe achieved, for example, by having the seawater sprayed downward intothe chamber, as the chilled air is introduced upward into the chamber.This arrangement is shown in FIGS. 16-18, and 25-30. With the counterflow using a downward spray of seawater, and an upward flow of chilledair, it is important to consider the effect of the opposing flows on theway the droplets circulate, freeze and settle within the chamber. Ineither instance, the difference between the two flow velocities, takinginto account the effects of gravity, and the size of the droplets, andthe temperature and volume rate of the chilled air flow, and size of thechamber, can help determine the extent to which the seawater dropletscan be sufficiently circulated, such that adequate cooling and freezingand settling of the droplets can be achieved. They must also fall to thebottom of the chamber to begin forming an ice mass in fairly shortorder, i.e., within less than a few seconds.

Accordingly, when considering a counter flow, one must consider theterminal fall velocity of the seawater droplet as it is being subjectedto the upward chilled air flow. A correlation of the terminal fallvelocity for water droplets in air is shown in FIG. 13. The smallerdiameter particles (shown below the line) will in many cases be blownupward and could be blown out of the system, and therefore, the nozzleconfiguration of the spray is preferably configured so that it does notproduce droplets that are too small. However, with most nozzles, acertain amount of the seawater droplets will inevitably be formed as aspray of tiny mist-like droplets, which will tend to be blown upward,although this preferably represents a very small fraction of theseawater output.

Consideration has been given to using about 7,151 SCFM chilled air, anda chamber having a 25 square feet cross sectional area vertical column,wherein the upward vertical velocity for the chilled air has beendetermined to be about 4.77 ft/sec. In such case, by taking into accountthe data supporting FIG. 13, it has been determined that seawaterdroplets that are greater than 325 microns will likely properly settledown slowly through the upward chilled air flow at that velocity. Bylooking at the chart in FIG. 13, however, it has been considered thatseawater droplets having a size of 4,000 microns in diameter, with 44ft/sec chilled air settling velocity, would be more acceptable. Dr. WaGao reported freezing 2,800 and 4,200 micron size droplets of piggerywastewater in mean times of about 7 seconds using minus 4 deg F. chilledair in her vertical wind tunnel. In the present invention, however, theseawater droplets are preferably frozen, from room temperature, i.e.,plus 40 degrees F., down to close to minus 6.2 degrees F. (eutectictemperature), in a much shorter amount of time, as little as about 0.2seconds, since chilled air at temperatures between minus 135 degrees F.to minus 175 degrees F. are used.

For the larger droplet sizes of the order of 4,000 microns diameter, itwill take more than 0.2 seconds to freeze the droplet to the core,assuming that the same temperature chilled air is used. At the outset,when the droplet is at +40 deg F. and the air may be between minus 175deg F. and minus 135 deg F., it might seem possible that there is astrong heat transfer and only 0.2 second is needed. Nevertheless, thiscalculation is not entirely accurate because heat exchange is takingplace as the droplet decreases in temperature and the local airincreases in temperature. Furthermore, it is assumed that the dropletinteracts with all the air that is needed to assure a proper heatexchange. However, droplet freezing data reported by Dr. Gao supportsthis short freezing time for an individual droplet in air streams thatare warmer. Consider the example for residence time in the counter flowchamber, wherein a 4,000 micron diameter droplet with a downwardsettling velocity of 44 ft/sec, encounters the slower upward velocity ofchilled air of 4 ft/sec in the chamber. The droplet will fall through a10 feet vertical height at 10 feet/(44 ft/sec−4 ft/sec)=0.25 seconds.Thus it is expected that the larger droplets will not complete therequired heat exchange until they deposit on the ice/snow mass andcomplete their heat exchange to attain the equilibrium temperature ofminus 6 deg F.

It can also be seen that the larger the droplet size, the greater theupward velocity of chilled air that can be used in the counter flowchamber, while still enabling the droplets to fall to the bottom of thechamber in a relatively short amount of time, which in one of theexamples being considered, is about 2.5 seconds. And, with a largerdroplet size, the longer it would take to freeze the droplet to thecore, assuming that the same temperature chilled air is used, wherein itis desirable for the temperature of the chilled air to be relativelylow, and the chilled air flow rate to be relatively high for a hightransfer rate to the droplet.

Although the nozzles will tend to be directed downwards into thechamber, as shown in FIGS. 16-18, through an orifice located on thechamber walls, chilled air will tend to flow upwards, by maintaining avent at the top of the chamber. By venting at the top, the chilled airintroduced into the chamber can only flow upwards, through the chamber,wherein this flow can be used to create the counter flow, against thefalling droplets. This trajectory gives the longest residence time andpermits coalescence of droplets that collide. The entry for the chilledair is located on the sides of the chamber so that the droplets will notstick to the injection mechanism. In the research work done on freezingdroplets, upward flowing chilled air was injected at an upward velocitysuch that the droplet settling velocity was matched and the dropletremained stationary for observation of the droplet properties duringfreezing.

The settling velocity of the droplets and the rapidity of the freezeprocess also determine the height of the settling chamber. Using thecounter flow arrangement, the taller the mixing chamber, the longer thedroplets will take to drop to the bottom, and therefore, the longer thedroplets will be exposed to the chilled air, to freeze. Furthermore, thephase diagram is an equilibrium diagram which assumes that sufficienttime is available to permit the separation of the different phases. Thefinal construction of the settling chamber therefore is preferablydetermined based on the phase separation efficiency of the system. If itis too optimistic, it may be necessary to either reduce the flow rate ofthe seawater through the nozzles, or increase the height of the settlingchamber, or volume flow rate of chilled air, etc.

It is also desirable to ensure that the ice particles remain separatedin the air so that they will freeze properly before they land andcoalesce at the bottom of the chamber to form an ice mass. If two ormore ice particles are allowed to merge together and combine in flight,they will tend to form larger droplets, which will require more time andcooling to freeze. Therefore, using the counter flow arrangement, it isdesirable to form seawater droplets that are far enough apart so thatwhen they are sprayed they will not merge together in the air.

Previous investigators have looked at two rain droplets colliding due tothe attractive force between them. They considered droplets 20 micronsin diameter and assumed that the initial separation is about 10 timesthe diameter rather than the usual assumption of 50 times the diameter.The 10 diameters separation produces a denser distribution of dropletsthat will more likely lead to coalescence, droplet growth, and rain.

Based on these ratios, if the separation between particles is 25 timesthe diameter, and the diameter is 4,000 microns, the preferredseparation distance would be 100,000 microns. This would mean that therewould be 1 particle in a cube that is 10 cm×10 cm×10 cm or 1 particleper liter. The above calculation would mean that the distribution ofthis cloud would need to be accomplished in a chamber volume that is1,026 feet tall and 25 square feet in cross sectional area, wherein thisstatic cloud would have a density of 1 particle per liter of air. Ifthis were the distribution of droplets in a cloud at high elevation, thedroplets would fall to the ground and not collide during their downwardtrajectory.

If the separation between particles is 10 times the diameter, and if thediameter is 4,000 microns, the separation distance would be 40,000microns. Based on the above calculations, the distribution of this cloudwould need to be accomplished in a chamber volume that is 260 feet talland 25 square feet in cross sectional area. If this were thedistribution of droplets in a cloud at high elevation, the dropletswould fall to the ground and possibly collide during their downwardtrajectory.

However, when introducing a nozzle spray that is continuously producinga seawater droplet cloud and causing continuous settling to occur usinga slowly moving upward air mass flow, such as one that flows up at 4feet per second, it has been determined that the height of the settlingchamber may be much less. In addition, when a droplet diameter of 4,000microns is used, they will not be affected as significantly by thedirection of the upward air flow, and therefore, will tend to deposit atthe bottom of the crystallization chamber, where it will complete itsheat exchange and some drainage in a few seconds. However, when dropletsof 200-micron diameter or less are used, they will tend to settle tooslowly, at a downward velocity of about 2 ft/sec, and therefore, thedroplets may not even deposit at the bottom of the crystallizationchamber. Accordingly, it will be necessary, in such case, to assure thatthe droplets are at least larger than 400-microns in diameter.Nevertheless, at the lower end of the size spectrum, these smaller sizedroplets will have a higher residence time, i.e., probably higher than2.5 seconds. Furthermore, as will be discussed later, the droplets willform a more porous ice mass when deposited at the lower temperaturesassociated with the incoming air at the bottom of the crystallizationchamber.

These are inherent disadvantages associated with the counter flowarrangement, insofar as the upward chilled air flow causes the dropletsto be forced upward and circulated for a greater period of time, whereinthey can more easily collide and merge together if the chamber isn'tlarge enough, and/or the density of the droplets is too high.

FIG. 16 shows an example of a counter flow and batch ice removal system,wherein chilled air is injected from the middle of the main chamber 141and flows upward. FIG. 16 shows a section view of main chamber 141, withpipes 143 and/or cavities extending around the chamber walls 145, forcirculating seawater and/or heated compressed air through the chamberwalls, as will be discussed, for heat exchange purposes. This embodimentshows that compressed air can be generated by turbo compressor 148, andthat the compressed air can be released and expanded by turbo expander150, wherein the chilled air that is produced can be introduced intochamber 141 near the middle 140. Additional compressors, and heatexchangers, etc., as discussed before, can also be provided.

Chilled air from turbo expander 150 is preferably directed upward as aresult of venting the chilled air at the top of chamber 141, i.e., thechilled air flow begins from about the mid point 140 of chamber 141 andexhausts at the top. The temperature, pressure and flow rate of thechilled air is preferably predetermined, and is a function of thefactors that are discussed herein.

Pre-chilled seawater that has been filtered and circulated through thechamber walls, as will be discussed, is preferably introduced intochamber 141 through a set of one or more nozzles 142, to form a spray ofseawater droplets, such as in the form of a droplet cloud. This ispreferably injected into the chamber from above, from the top 147 ofchamber 141, and in a downward direction. The temperature, pressure andflow rate of the seawater droplets is preferably predetermined, and is afunction of the factors that are discussed herein.

This configuration enables the chilled air and seawater droplets to beintroduced in opposite directions into the chamber 141, and circulated,wherein the droplets can be further cooled by the chilled air throughheat exchange within the chamber. The nozzles 142 are preferablydesigned to distribute the droplets toward the center, such that the iceparticles are kept away from the chamber walls, and so that the ice masstends to form in the center of the chamber, such as in the form of aninverted cone shape. In this embodiment, the exhaust chilled air isallowed to exit chamber 141 through an exhaust at the top 147, whereinthe exhaust chilled air can then be used for other cooling purposes,such as air conditioning.

The warmer intake temperature of the seawater and/or heated air from theturbo compressor 148 are preferably circulated within the chamber walls145 to help keep the ice droplets forming in the chamber 141 fromcollecting on the walls 145, and regulate the temperature inside thechamber 141, i.e., to help maintain a more consistent temperatureinside.

Seawater that has been filtered, for example, can be introduced by apump into pipes 143 and/or cavities at near the mid-point 152, such thatit circulates upward through the upper half of the chamber walls 145,and can exit near the top, at point 153, where the pre-chilled seawatercan be distributed by nozzles 142, for introduction into chamber 141.Seawater is preferably circulated through the upper pipes 143 extendingaround chamber 141, wherein as the seawater circulates, it is pre-cooledby heat transfer with the cold chamber walls 145, before it is releasedinto the main chamber 141 via nozzles 142. In this respect, the seawateris preferably (1) chilled as it circulates through the intake pipes 143that surround the main chamber 141, (2) chilled as seawater droplets areejected through a spray nozzle inside the main chamber 141, and (3)further chilled when the freezing seawater droplets are deposited on amound to form an ice mass at the bottom of the chamber 141.

Heated air from the turbo compressor 148 can be introduced into thepipes 155 and/or cavities at a low point 154, such that it circulatesdownward through the lower section of chamber walls 145, and can exit atthe bottom 156, wherein the cooled compressed air can then bedistributed back to turbo expander 150, to help keep the compressed aircool. In this respect, the pipes 155 are preferably adapted to maintainthe compressed air in its compressed state, which allows the actual airthat is expanded by turbo expander 150 to be pre-cooled, so that theresultant chilled air can be made colder. In effect, heated compressedair from turbo compressor 148 can be circulated to keep the ice massfrom sticking to the chamber walls, and, as the air circulates, it iscooled by heat transfer from the chilled chamber walls, wherein thepre-cooled air is then circulated back to turbo expander 150, whereinthe air is super cooled and introduced into the main chamber 141, tofreeze the seawater droplets.

The location of the pipes and/or cavities can be modified, i.e., theseawater can be circulated through the entire chamber, or the lowersection, and/or the heated air can be circulated through the entirechamber, or the upper half, depending on the needs of the system.Preferably, much of the pre-cooling of the seawater and heated airoccurs when it is in the pipes and/or cavities and there is thereby anexcellent means of transferring heat within the chamber walls.

The bottom of the chamber is preferably adapted to allow theconcentrated salt brine to be collected and then removed, through vent158, wherein the ice mass will form on top of the salt brine, and floatthereon, due to the lower density of the ice, and the higher density ofthe brine. A basket 159 can be provided at the bottom of the chamber sothat the ice mass can easily be removed without having to stop thesystem. In this respect, the bottom of the chamber 141 is preferablyadapted with an opening, which allows basket 159 to be removed, whereinthe ice mass can then be thawed to produce fresh drinking water.Alternatively, the bottom of the chamber 141 can be designed to have adrop down door, such as with a hinge, such that without having to stopoperating the system, the door can be lowered, to allow the ice mass,and any remaining collected brine, to be removed from chamber 141. Insuch case, there is preferably a conveyor system under chamber 141 whichallows the ice mass to be transported to where it can be thawed andmelted to produce fresh drinking water.

FIGS. 17 and 18 also show a counter flow system with a similar chamber80 with chilled air introduced near the midpoint 82, wherein the nozzles84 are adapted to introduce seawater from above. These drawings moreclearly show the shape of the ice mass 86 forming at the bottom to bemore of an inverted cone shape, as a result of directing the nozzles 84toward the center of the chamber 80. This embodiment also shows a pistonembodiment which can be used to lower the ice mass down from the chamberwhen it is desired to be removed. It also shows that the entry point 82of the chilled air should be higher than the highest possible point ofthe ice mass. This is designated by the reference “H” which is thedistance from the bottom of the chamber to the chilled air entry point.This is necessary to assure that the injected chilled air does notimpinge on the ice mass and surrender its chilling properties into theice mass rather than into the air in the settling chamber 80. Theinjected air must enter the settling chamber 80 and immediately rise tothe top of the chamber and interact with the falling seawater droplets.FIG. 18 also shows that a separate heating unit can be incorporated intothe chamber walls near the bottom to help keep the ice mass, and anyfalling ice particles, from freezing onto the chamber walls.

There is a zone at the bottom of the settling chamber below the chilledair injection point that will contain a dead air regime wherein aircirculates in eddies. These eddies will sap some of the intake chilledair and will return some of the eddy air back into the main upwardairflow. Because the eddy flows may undesirably maintain the ice massand saline water at below the eutectic temperature, resulting in some ofthe salt crystallizing and depositing at the bottom of the salinesolution, the value of H should be determined to ensure that the icemass will remain at the appropriate temperature, which, in the preferredembodiment, is slightly above the eutectic point. Note that the shape ofthe developing ice mass is preferably conical-like, although any shapethat allows the salt brine to runoff the sides or down through its poresis contemplated, as will be discussed. This facilitates the depositionof ice crystals and the runoff of the saline solution associated witheach ice crystal.

It is also desirable to maintain a liquid annular gap around theperiphery of the ice mass as it develops and also to facilitate itsdisplacement during removal. As the droplets deposit on the ice mass,the mass separates into its two phases, ice crystal and saline solution.Because of the conical surface of the ice mass, the liquid can rundownhill and outward toward the walls of the settling chamber.Accordingly, it is desirable for the ice mass to have a gap between theice mass and the settling chamber in order for the draining liquid torun off the ice mass and into the saline solution underneath. Inaddition to building in a heat exchange system, using pipes and/orcavities within the chamber walls, as discussed above, a local heatercan be provided in the wall of the settling chamber, at the bottom ofthe chamber, which can be turned on to supply just enough local heatingto maintain the required gap.

FIGS. 17 and 18 show a piston that can be used to lower the ice mass, sothat it can be removed from the chamber 80, wherein this annular gap canfacilitate the movement of the ice mass through the settling chamber.The height of the settling chamber is preferably designed to supply theresidence time to facilitate the transfer of chilling energy from theair to the seawater droplets during a period measured in seconds.However, the main separation of the ice from the saline solution occurson the ice mass where it remains for longer time periods, ranging fromminutes to hours.

E. Co-Flow Arrangement:

In addition to blowing the chilled air upward against the fallingdroplets, i.e., “Counter-flow,” as in the systems discussed above,additional embodiments have been developed in which the chilled air isblown in the same direction as the seawater droplets, referred to as“Co-flow.” The co-flow arrangement is shown in FIGS. 14-15, and 31-34.The advantages and disadvantages of both are discussed herein.

A downward flow of chilled air into the chamber is advantageous becausethe air is at its coldest temperature at the moment it hits theseawater, i.e., as it is being sprayed downward from the top of thechamber. This exposes the droplets to temperatures that aresubstantially lower than the eutectic temperature, and helps to beginthe flash freezing process of the seawater quickly, which helps form icefaster. This can also help to keep the droplets from sticking togetherif and when they collide, as they would if the density of the dropletsis too high, or the chamber size is too small.

As the droplets fall, which is a function of the height of the chamber,and begin to absorb the cold air, i.e., which in turn freezes thedroplets, the air begins to warm up, so that by the time the dropletsreach bottom, the air is not as cold as it was when it was introducedinto the chamber, which is advantageous because it prevents the iceparticles from becoming too cold, which can cause the entire brine tofreeze. By keeping the temperature of the mixture at the bottom of thechamber slightly above the eutectic point, the brine is prevented fromfreezing completely, which, as will be discussed, will allow more of theliquid salty brine solution surrounding the ice particles to runoff andseparate from the ice particles.

The downward flow of chilled air also prevents the droplets from beingsuspended in mid-air for too long, which can happen if the chilled airis blown against the falling droplets as in the case of the counter-flowarrangement. Exposing the droplets to chilled air for too long can makeit difficult to control and accurately regulate the precise temperaturein the chamber, as well as the temperature of the droplets, which isnecessary to maintain a proper consistency at the bottom. For example,in many situations, the freezing state of the seawater may not be thesame from one location inside the chamber to another, i.e., some iceparticles may end up being exposed to the chilled air for too long, inwhich case they may be too cold, while others may not be exposed longenough, in which case they would not be cold enough. This problem can beamplified when the size of the droplets differ as they are emitted fromthe nozzles, thereby causing the droplets to freeze at different rates.

With the downward co-flow process, many of these problems can beavoided. Nevertheless, one potential downside is that by exposing theseawater droplets to a blast of chilled air in the same direction as thefalling droplets, the droplets may travel too quickly to the bottom ofthe chamber, which means that there will be less residence time for thedroplets to freeze. One solution to this problem is to use super coldchilled air that can act on the droplets quickly, to ensure that by thetime the droplets reach the bottom of the chamber, they are at theproper temperature. Another is to use pre-chilled seawater to form thedroplet cloud so that less time is required for the seawater droplets tofreeze and/or reach the eutectic point, and therefore, less exposuretime is needed.

Another is to regulate the size and flow rate of the seawater droplets,and the chilled air flow, so that the droplets do not travel as quicklydown to the bottom. For example, in one embodiment, the co-flowingchilled air can be introduced into the chamber at a reduced velocity,such as at about 4 feet per second downward, such that as the dropletsare introduced into the chamber, and if the droplets are small enough,they can actually decelerate in flight. This can occur because, even ifthe droplets are emitted at a relatively high velocity, if they aresmall enough, they can be significantly affected by the slower movingdownward air mass, wherein, even if they start out at a velocity, of,say, about 26 feet per second, into a 14.67 psia atmosphere, they mayslow down, in response to the much slower air flow.

Nevertheless, with this flow rate, the residence time of the droplet'sflight in the chamber will likely be relatively short, i.e., the time ittakes for the droplet to fall from the top of the chamber down to wherethe droplets deposit onto an ice mass at the bottom of the chamber.Whether the droplets are relatively large (up to 5,000 microns) and havea 55 ft/sec settling velocity, or small (as little as 200 microns) andhave a 2 ft/sec settling velocity, the downward air flow of 4 feet persecond will result in a residence time of either 0.16 seconds for the5,000 micron droplet (10 feet÷(55 ft/sec+4 ft/sec)=0.16), or 1.6 secondsfor the 200 micron droplet (10 feet÷(2 ft/sec+4 ft/sec)=1.6) in achamber that is 10 feet tall. Accordingly, there is still the need touse super chilled air, and/or pre-cooled seawater, as discussed.

As mentioned above, residence time (the flow time during which thermalinteraction and thermal exchange occurs between the seawater droplet andthe surrounding chilled air flow) is one of a number of key parameterscontrolling the freezing of the pure water constituent of the seawaterdroplet and promoting separation of the resultant ice crystal particlefrom the residual brine. Residence time depends on the seawater dropletvelocity down the desalination chamber, as well as on the desalinationchamber height. The chamber height is therefore established based on therequirement that particle water freezing is completed and its separationfrom the residual brine is accomplished.

Consider the example wherein the turbo expander supplies airflow at5,297 SCFM, and uses a 4 ft/sec vertical velocity in the crystallizationchamber, so that the chamber has a required 5.3 ft diameter. Considerthat the height of the chamber is 10 ft. The following calculationassumes a 2.5 seconds residence time. The same calculation must beperformed for other residence times.

-   -   5,297 scfm airflow    -   4 ft/sec vertical velocity in chamber    -   240 ft/min vertical velocity in chamber    -   22.1 sq ft    -   5.3 ft diameter    -   2.5 sec residence time    -   10 ft path length (height of chamber)

It is also necessary to assure that the droplets have sufficient spacingto assure collision avoidance. In the example we have been using, andrequiring the ratio of the air diameter to droplet diameter to be 16:1,the following table shows the cloud parameters inside thecrystallization chamber, for both large and small droplets:

The top table below shows that for a 4 ft/sec transit velocity (of thedownward chilled air flow), the 5,297 SCFM requires a chamber diameterof 5.3 feet. For a droplet size of 4,000 micron and 5,297 SCFM air flow,the spacing between droplets is 16 droplet diameters. This correspondsto a reasonable cloud description with independent flight paths. Thelower table below shows the same is true for the droplet diameters of200 microns, except that there are more of them. 4,917 #/hr seawater4,000 microns 64 #/cu ft seawater 0.4 cm 76.8 cu ft/hr seawater 1.57E−01in diameter 1.28 cu ft/min sea water 1.18E−06 cu ft volume of droplet5,297 scfm air 6.40E+01 #/cu ft 16.1 dia std air/dia seawater 7.57E−05#/droplet 5.3 ft diameter chamber 1.08E+06 droplets per min 4.0 ft/secair 5297 scfm air 4.90E−03 scf air/droplet

4,917 #/hr seawater 200 microns 64 #/cu ft seawater 0.02 cm 76.8 cuft/hr seawater 7.87E−03 in diameter 1.28 cu ft/min sea water 1.48E−10 cuft volume of droplet 5,297 scfm air 6.40E+01 #/cu ft 16.1 dia air/diaseawater 9.47E−09 #/droplet 5.3 ft diameter chamber 8.66E+09 dropletsper min 4.0 ft/sec air 5297 scfm air 6.12E−07 scf air/droplet

For the co-flow system, a pressure difference of 10-psid will spray adroplet into the chamber at 22.8 ft/sec. A diameter droplet diameter of4000 micron has a settling velocity of 44 ft/sec. Thus the large dropletwill spray into the chamber at a much higher velocity than the local airvelocity of 4 ft/sec and tend to be momentarily accelerated from 22.8ft/sec to 44 ft/sec. For a 10 ft path length in the air the residencetime would then be about 0.25 seconds. Thus a large droplet of 4,000microns may deposit too quickly for complete heat exchange to occurbetween the droplet and the chilled air, although most of the heatexchange will have occurred if a relatively high heat transfercoefficient applies. The continuous flow of the cold air over thedeposited ice mass will complete the remaining heat exchange.

For the co-flow air system, a pressure difference of 40-psid will spraya droplet into the chamber at 45 ft/sec. A diameter droplet diameter of200 micron has a settling velocity of 2 ft/sec. Thus the small dropletwill spray into the chamber at a much smaller velocity than the localair velocity of 4 ft/sec and tend to be momentarily decelerated from 45ft/sec to 4 ft/sec. For a 10 ft path length in the air the residencetime would be about 2.5 seconds. Thus the small droplet will deposit onthe bottom of the crystallization chamber with complete heat exchange atabout minus 6 degrees F.

Another consideration that should be made in setting up the system isthe fact that it may be difficult to accurately control the exact sizeof the seawater droplets emitted by the nozzles. Although flow rates andvelocities can be accurately controlled, the actual size of the seawaterdroplet is not as easily regulated. Therefore, the system settingsshould be designed to take this into account. That is, whether thedroplets are small or large, the velocity of the air mass, as well asthe pressure and velocity of the droplets should be controlled so thatthe end result is as consistent as it can be. When the droplets aresmaller, they will tend to be more affected by the air mass, and lessaffected by the original emission speed, and therefore, considerationmust be made to account for this, i.e., the fact that they will tend tobe brought down at a slower rate than a relatively large droplet. At thesame time, when the droplets are larger, they will tend to be lessaffected by the air mass, and more affected by the emission speed, andgravity, and therefore, consideration must be made to account for thefact that they will tend to be brought down at a relatively higher rate.

In this respect, the present invention preferably contemplates that evenrelatively large droplets on the magnitude of up to about 4,000 to 5,000microns in diameter can be sufficiently affected by the air flow, andtherefore, the residence time can be controlled to a sufficient level.Although the rate at which each different size droplet falls to thebottom of the chamber will differ, depending on the size and mass of thedroplets, and therefore, the exposure time of each different sizedroplet may differ, the present invention contemplates that the settingscan be adapted to ensure that the droplets are exposed to the chilledair sufficiently, and when the ice particles reach bottom, they will benear the eutectic temperature, wherein the droplets will form icecrystals, coalesce and form an ice mass, and the brine salt solutionwill runoff properly, as will be discussed. This system also permitsempirical control of the flow because one can control the flow of thechilled air so that the final conditions are as desired.

One of the goals of the system is for the final equilibrium temperatureafter the droplets deposit on the bottom of the chamber to beconsistently at slightly above the eutectic temperature. This means thatregardless of the droplet size, the condition of the circulation withinthe chamber should be such that it will cause the mass rate of thechilled air flow to eventually match the mass rate of the seawaterdroplet flow, to effect the best possible heat exchange, so that thefinal result will be that the exhaust air within the chamber and theaccumulating ice particles will be at the ideal temperature, i.e., closeto the eutectic temperature. Nevertheless, given that a perfect heatexchange is not likely, the more likely scenario is that the exhaustchilled air will be colder than the eutectic temperature, and the icemass at the bottom will be warmer than the eutectic temperature, whichis a result that is acceptable.

Of course, proper heat exchange must take into account the heat transfercoefficient for the seawater droplets, which is difficult to determinegiven that each droplet size might differ. Moreover, within the chamberitself, as the droplets fall, each droplet is getting colder, while theair is getting warmer, so that at each subsequent instant during theprocess, the heat transfer coefficient is changing. The heat transfercoefficient between the seawater droplet and the surrounding chilledairflow is a critical parameter controlling the freezing of the purewater constituent of the seawater droplet and its separation from theresidual brine. The heat transfer coefficient is a function of thediameter of the seawater droplet and its density, the density of thechilled air, the temperature of both, the chilled air and the waterdroplet, the relative velocity between the seawater droplet and thesurrounding chilled airflow, and the residence time of the seawaterdroplet within the surrounding airflow. The values of these parameterswill change along the droplet flow path, and so will the resultant heattransfer coefficient.

The table in FIG. 35 shows that the large 4,000-micron droplet will havea core temperature between minus 56.6 degrees F. and plus 8.59 degreesF. in a flight of 0.2 seconds, depending upon the heat transfercoefficient. The heat transfer coefficient is likely closer to the 50BTU/(HR SQFT F) value. The small 200-micron droplet will have a coretemperature between minus 120.8 degrees F. and plus 39.9 degrees F. in aflight of 0.2 seconds, depending upon the heat transfer coefficient. Theheat transfer coefficient is likely closer to the 50 BTU/(HR SQFT F)value. Thus it can be expected that the droplets, large and small, willbe between minus 56.6 degrees F. and minus 120.8 degree F., althoughthis is not likely to happen since the temperature of the chamber iswarmer near the bottom, so that the assumption of a constant minus 121degrees F. air temperature is false. What the calculation is meant toshow, however, is that a 4 second flight time in the crystallizationchamber should permit the complete mixing of the air and the droplets sothat the final equilibrium temperature of the air will approach somewhatcooler than minus 6 degrees F. and the droplets will approach slightlywarmer than minus 6 degrees F. when deposited on the bottom of thecrystallization chamber. Thus, the end result in the desalinationprocess is that the entry droplets smoothly decrease their temperatureto slightly above minus 6 degrees F. and the air is warmed smoothly toless than minus 6 degrees F.

It should be clear that the smallest droplets will likely freeze acrosstheir entire volume relatively quickly, given that the chilled air iscoldest at the top of the chamber, wherein there is not likely to be adelay in converting the liquid seawater to a solid. Although it is notdesirable for the droplets to become too cold, this is acceptable giventhat by the time the frozen droplet reaches the bottom of the chamber,the temperature of the air, and of the ice mass, will be such that thedroplet will warm back up again to slightly above the eutectic point,thereby avoiding the freezing of salt crystals, and allowing for thesalt brine solution to adequately runoff, rather than being trappedwithin the ice mass.

In the case of larger droplets, however, the droplets will be moreaffected by the differences in temperature from the top to the bottom.Moreover, with larger droplets, there is a greater variance in how thedroplet itself will freeze. That is, as far as exposure to coldtemperatures is concerned, the larger droplets will be exposed to thecoldest temperature from the outside in, i.e., the outside of thedroplet will become colder faster than the inside of the droplet. On onehand, this might indicate that the salt will tend to be forced towardthe center, while the fresh water on the outside might begin to freeze.On the other hand, studies have shown that when the water dropletreaches a certain temperature across its volume, the fresh water withinthe droplet actually freezes in the center first, and the moreconcentrated salt brine solution attaches itself to the outer surface ofthe ice crystal.

Other studies indicate that large droplets will freeze from the outside,forming an outer ice shell. As the shell thickness grows inward due tofurther freezing, it increases the pressure within the central liquidcore, thus resulting in cracking and fragmenting of the brittle iceshell. The liquid brine then flows to the outside of the ice shell asthe freezing continues the inward growth of the ice. The inner liquidcore then coats the outside of the frozen fresh water droplet. The netconclusion is that for large droplets the inner liquid core containingsalt will flow to the outside of the frozen particle of fresh water iceand will deposit on other similar configurations of ice particle coatedwith liquid brine. The attachment of these frozen spheres produces aporous structure that allows the liquid brine to drain down from thedeposited mass and drain through a perforated surface to a collectionpan.

Although pure water freezes at 0 degrees C., the freezing point can belowered by dissolving salt into the water. Then, if the mixture iscooled to below the new freezing point, water crystals will begin toform. As a result, the remaining salt solution becomes furtherconcentrated, until the salt saturation point is reached. Thisintersection of the freezing point line and the saturation point line isreferred to as the eutectic point, as shown in FIG. 6. Below theeutectic point, salt crystals will be formed in addition to the icecrystals, although in forming the final ice mass, the present inventionpreferably operates above the eutectic point, to avoid the formation ofsalt crystals.

When the solution freezes, the water molecules tend to form the moststable crystal arrangement if there are no foreign particles present.When a solution containing minerals is cooled to the freezing point, thewater molecules begin to form ice crystals that tend to excludeparticles that are unlike the water molecules. For example, as saltwaterfreezes, salt is excluded because salt has a different crystallinestructure than water. This is sometimes called brine rejection. Saltforms cubic crystals (with four sides), whereas ice is hexagonal, orsix-sided. Among all the molecules in a volume of cold, salty water,there are instances of water molecules that are next to each other, awayfrom any of the Na⁺ or Cl⁻ ions. These tend to stick together, whilethose molecules with Na⁺ or Cl⁻ ions will be less likely to stick, or tostay stuck. This produces fresh water ice crystals, which separate fromthe slightly saltier liquid water. There are 13 different crystalformations of frozen water depending upon the extent of the coldtemperature. Some of the crystal formations are quite porous and willpermit liquids to flow through the open channels that are formed.

At room temperature, liquid water becomes denser as the temperature islowered, just like other substances. But at 4 degrees C., just abovefreezing, water reaches its maximum density, and then, as the watercools further toward its freezing point, the liquid water, understandard conditions, expands to become less dense. The physical reasonfor this is related to the crystal structure of ordinary ice, known ashexagonal ice. This special property of water is put to good use in theprocess of the present invention. As salt crystals form near theeutectic point, they sink to the bottom of a solution while the icecrystals rise to the surface. The result of the process is a separationby physical means, allowing the two components of the solution to bereadily isolated.

In the downward Co Flow process shown in FIGS. 14 and 15, the chilledair is preferably maintained at an extremely low temperature, such as atabout minus 168 degrees F. with about 14.67-psia discharge pressure. Thepreferred range is between minus 135 degrees F. and minus 175 degrees F.A one-stage turboexpander will generate minus 135 degrees F. whereas atwo-stage turboexpander will generate minus 175 degrees F. This chilledair preferably contacts the seawater droplets which are injected at areduced temperature as well, such as about 30 degrees F. to 40 degreesF., at the top of the crystallization chamber 101. As the mixture ofchilled air and seawater droplets move downward in the chamber 101, thechilled air is warmed by the seawater droplets and the seawater dropletsare chilled by the co-flowing surrounding air. The mass flow of thechilled air and the mass flow of the seawater droplets are designed toresult in a final equilibrium temperature of slightly warmer than minus6.2 degrees F., the eutectic temperature for saltwater. Nevertheless,because perfect heat exchange is not likely to occur, for reasonsdiscussed above, it is likely that the chilled air that is cycled out ofthe chamber is colder than the eutectic temperature, and that thedroplets are slightly warmer than the eutectic temperature, which isdesirable.

There may be a time delay before freezing can set in. It is assumed thatthe system will be adapted such that the injected seawater can bereduced to close to minus 6 degrees F. by the time it reaches bottom,within a residence time of less than 2.5 seconds. Some will freezesooner, and others may need the entire 2.5 seconds, but the system ispreferably adapted so that as the droplets collect at the bottom, theresidual temperature of the droplets and resulting ice mass will beslightly above minus 6 degrees F. Much of the heat exchange process willhave occurred before the droplet formation can freeze completely.Another advantage of the co-flow system is that the crystallizationchamber can be made smaller, since the droplets will freeze faster.

In FIGS. 14 and 15, examples of the co-flow desalination system of thepresent invention are shown. FIG. 14 shows a section view of the mainchamber 101 with pipes 103 and/or cavities extending around the walls105 thereof for circulating seawater and/or heated compressed airthrough the chamber walls. The warmer temperature of the seawater and/orheated air from the compressor helps to keep ice from collecting on thewalls of the chamber, and regulate the temperature inside the chamber,to help maintain a more consistent temperature inside the chamber.Seawater that has been filtered, for example, can be introduced into thepipes 103 and/or cavities at the bottom 110, such that it circulatesupward and around through the lower half of the chamber walls, and canexit at near a mid-point 112, where the pre-chilled seawater can bedistributed upward, to nozzles 108, for introduction into chamber 101.Heated air from the turbo compressor can be introduced into the pipes103 and/or cavities at about the mid-point 114, such that it circulatesupward and around through the upper half of the chamber walls, and canexit at the top 116, wherein the cooled air can be distributed back tothe turbo expander, to help keep the compressed air cool.

The heat transfer from the cold temperature inside the chamber to thepipes and/or cavities surrounding the chamber helps to cool the seawaterand/or heated air, which helps to pre-cool the seawater before it issprayed into the chamber, and/or pre-cool the heated air before beingchilled by the turbo expander and introduced into the chamber.Preferably, much of the pre-cooling of the seawater and heated airoccurs when it is in the pipes and/or cavities and there is thereby anexcellent means of transferring heat. The location of the seawaterand/or heated air pipes and/or cavities can be modified, i.e., theseawater can be circulated through the entire chamber, or the upperhalf, and/or the heated air can be circulated through the entirechamber, or the lower half, depending on the needs of the system.

Chilled air from the turbo expander is preferably directed downward andintroduced into the chamber 101 from above, at the top 107 of chamber101. The temperature, pressure and flow rate of the chilled air ispreferably predetermined, and is a function of the factors that arediscussed herein. Pre-chilled seawater that has been filtered andcirculated through the chamber walls is preferably introduced into thechamber through a set of one or more nozzles 108, to form a spray ofseawater droplets, such as in the form of a droplet cloud. This ispreferably injected into the chamber from above, from the top 109 of thechamber. The temperature, pressure and flow rate of the seawaterdroplets is preferably predetermined, and is a function of the factorsthat are discussed herein.

This configuration enables both the chilled air and seawater droplets tobe introduced in the same direction into the chamber 101, andcirculated, wherein the droplets can be cooled by the chilled airthrough heat exchange within the chamber. The nozzles 108 are preferablydesigned to distribute the droplets toward the center, such that the iceparticles are kept away from the chamber walls, and so that the ice masstends to form in the center of the chamber, such as in the form of aninverted cone shape. In the embodiment of FIG. 14, the exhaust chilledair is allowed to exit chamber 101 through a lower exit point 111, intoside chamber 113, which allows the chilled air to circulate downwardthrough the chamber 101, wherein the exhaust chilled air can then beused for other cooling purposes, such as air conditioning. Thisembodiment is intended for use with a continuous extrusion rotatingauger that helps remove the ice mass from the bottom of the chamber. Thebottom of the chamber is adapted to allow the concentrated salt brine tobe collected and then removed, wherein the ice mass will form above thesalt brine, and float thereon due to the lower density of the ice, andthe higher density of the brine.

FIG. 15 shows a section view of the co-flow and batch ice removalsystem, wherein chilled air is injected from the top of the mainchamber. FIG. 15 shows a section view of the main chamber 121 with pipes123 and/or cavities extending around the walls 125 thereof forcirculating seawater and/or heated compressed air through the chamberwalls. This embodiment shows compressed air being generated by turbocompressor 118, and a turbo expander 120 for releasing and expanding thecompressed air, wherein the chilled air is introduced into chamber 121at the top. Additional compressors, and heat exchangers, etc., asdiscussed before, can also be provided.

The warmer temperature of the seawater and/or heated air from thecompressor helps to keep ice from collecting on the walls of thechamber, and regulate the temperature inside the chamber, to maintain aconsistent temperature inside the chamber. Seawater that has beenfiltered, for example, can be introduced by a pump into the pipes and/orcavities at the mid-point 130, such that it circulates upward and aroundthrough the upper half of the chamber walls, and can exit near the top,at point 132, where the pre-chilled seawater can be distributed tonozzles 122, for introduction into chamber 121. On the top of the mainchamber, seawater is preferably circulated through the upper pipes 123extending around the chamber 121, wherein the relative warmth of theseawater helps to prevent ice from collecting on the chamber walls 125.Likewise, as the seawater circulates, it is pre-cooled by heat transferwith the cold chamber walls 125 before it is released into the mainchamber 121 via the nozzles 122. Although the seawater droplets arecooled and frozen using the interaction with the chilled air, asignificant portion of the seawater temperature drop can be achieved bypassing the seawater through the tubes 123 surrounding the chamber 121.

Heated air from the turbo compressor 118 can be introduced into pipes133 and/or cavities at a low point 134, such that it circulates downwardand around through the lower section of the chamber walls, where the icemass collects, and can exit at the bottom 136, wherein the cooledcompressed air can be distributed back to the turbo expander 120, tohelp keep the compressed air cooler. In this respect, pipes 133 arepreferably adapted to maintain the compressed air in its compressedstate, which allows the actual air that is expanded by turbo expander120 to be pre-cooled, so that the resultant chilled air can be made evencolder. Heated compressed air from the turbo compressor 118 helps keepthe ice mass from sticking to the chamber walls. As the air circulates,it is cooled by heat transfer from the chilled chamber walls, whereinthe pre-cooled air is then circulated to turbo expander 120, wherein theair is super cooled and introduced into main chamber 121 to freeze theseawater droplets.

The heat transfer from the cold temperature inside the chamber to thepipes and/or cavities surrounding the chamber helps to cool the seawaterand/or heated air, which helps to pre-cool the seawater before it issprayed into the chamber, and/or pre-cool the compressed air beforebeing released and chilled by the turbo expander and introduced into thechamber. Preferably, much of the pre-cooling of the seawater and heatedair occurs when it is in the pipes and/or cavities and there is therebyan excellent means of transferring heat from the seawater and heated airinto the chamber walls and chamber air. The location of the seawaterand/or heated air pipes and/or cavities can be modified, i.e., theseawater can be circulated through the entire chamber, or the lowersection, and/or the heated air can be circulated through the entirechamber, or the upper half, depending on the needs of the system.

Chilled air from the turbo expander is preferably directed downward andintroduced into chamber 121 from above, at the top 127 of chamber 121.The temperature, pressure and flow rate of the chilled air is preferablypredetermined, and is a function of the factors that are discussedherein. Pre-chilled seawater that has been filtered and circulatedthrough the chamber walls is preferably introduced into the chamberthrough a set of one or more nozzles 122, to form a spray of seawaterdroplets, such as in the form of a droplet cloud. This is preferablyinjected into the chamber from above, from the top 127 of chamber 121.The temperature, pressure and flow rate of the seawater droplets ispreferably predetermined, and is a function of the factors that arediscussed herein.

This configuration enables both the chilled air and seawater droplets tobe introduced in the same direction into chamber 121, and circulated,wherein the droplets can be further cooled by the chilled air throughheat exchange within the chamber. The nozzles 122 are preferablydesigned to distribute the droplets toward the center, such that the iceparticles are kept away from the chamber walls, and so that the ice masstends to form in the center of the chamber, such as in the form of aninverted cone shape. In this embodiment, the exhaust chilled air isallowed to exit chamber 121 through one or more air ports 137, whichallows the chilled air to circulate downward through chamber 121,wherein the exhaust chilled air can then be used for other coolingpurposes, such as air conditioning. The bottom of the chamber is adaptedto allow the concentrated salt brine to be collected and then removed,through vent 139, wherein the ice mass will form on top of the saltbrine, and float thereon, due to the lower density of the ice, and thehigher density of the brine.

A basket 138 can be provided at the bottom so that the ice mass caneasily be removed from the chamber without having to stop the system. Inthis respect, the bottom of the chamber 121 is preferably adapted withan opening so that basket 138 can be removed, wherein the ice mass canthen be thawed to produce fresh drinking water. Alternatively, thebottom of the chamber 121 can be designed to have a drop down door, suchas with a hinge, such that without having to stop operating the system,the door can be lowered, to allow the ice mass, and any remainingcollected brine, to be removed from chamber 121. In such case, there ispreferably a conveyor system under chamber 121 which allows the ice massto be transported to where it can be thawed and melted to produce freshdrinking water.

In FIGS. 31-34, the desalination system 40 of the present invention ispreferably adapted to remove salt and other impurities from seawater 60.In this embodiment, the desalination system 40 preferably comprises acrystallization chamber 41, which can be used to remove salt and otherimpurities, wherein purified water can be produced thereby. Thecrystallization chamber 41 is preferably an insulated containerspecially adapted to maintain cold temperatures inside, and to allowseawater 60 and chilled air 50 to be introduced and mixed therein, aswell as ice and concentrated brine to form at the bottom. Thecrystallization chamber 41 can be similar to those disclosed in U.S.provisional application Nos. 60/789,415, filed Apr. 5, 2006, 60/794,190,filed Apr. 21, 2006, and 60/832,777, filed Jul. 24, 2006, which are allincorporated herein by reference.

The desalination system 40 preferably injects seawater 60 into thecrystallization chamber 41, preferably in the form of a mist, or spray62, wherein the chilled air 50 from the turbo expander is preferablyintroduced into the chamber 41, thereby exposing the mist or spray 62 tovery cold air. This causes the seawater droplets 62 to be super chilled,and flash frozen, thereby forming super cooled ice particles 63 thatdrop onto the bottom 64 of the chamber. The seawater droplets 62 arepreferably but not necessarily introduced at the top 65 of the chamber,and the chilled air 50 is either 1) introduced near the middle of thechamber and directed upward, or 2) introduced into the chamber fromabove, which creates a down draft, which forces the seawater droplets 62down to the bottom faster. The factors that determine which to usedepends on how quickly the seawater needs to be frozen, which isdependent on how cold the seawater 60 is before it enters chamber 41,how cold the chilled air 50 is, the size of the chamber 41, how theseawater droplets are exposed to and circulate with the chilled air, andthe amount of each that is being introduced, etc.

The freezing of the seawater 60 preferably enables buoyant pure waterice particles 63 to be formed, with trace amounts of salty brine 67adhering thereto, with the objective being to leave behind the salt andother impurities in the salty brine 67, at the bottom 64 of the chamber41. The desalination system 40 preferably removes the ice particles 63from the salty brine 67, which is denser than the ice particles 63, sothat gravity can help separate the brine 67 from the ice particles 63,and cleans the ice particles 63, in one of at least two ways.

First, the ice particles 63 can form a large ice mass 66, by allowingthe ice particles 63 to accumulate at the bottom of the chamber 41,i.e., as they fall on top of each other. Over time, as the ice particles63 fall and they stick together, they will collectively form an ice mass66, which will tend to float on top of the salty brine 67, which isdenser than the ice mass 66. In this respect, preferably, the system isadapted so that ice particles 63 will form a conical shape ice mass 66,by introducing seawater droplets 62 into the center of the chamber 41,wherein ice particles 63 formed thereby will also accumulate in thecenter of the chamber. This advantageously enables the salty brine 67that encapsulates or adheres to each pure water ice particle 63 to rundown the sides, rather than being trapped inside ice mass 66 i.e., inpockets or crevices that might otherwise form on mass 66 as itsolidifies. By forming a cone shaped ice mass 66, the brine 67 thatadheres to each ice particle 63 will simply run off down the sides,rather than being trapped in mass 66, so that salty brine 67 can beeffectively separated from ice mass 66 as needed. On the other hand,studies have shown that the ice mass that forms may form channels andvoids throughout the mass so that any accumulated salt brine 67 couldsimply pass through the mass, via the channels and voids, without beingtrapped in the mass. The ice mass, in this respect, looks more likesnow, and forms a porous mass that allows the brine to pass through. Theice particles that are formed and fall onto the ice mass are typicallyat about minus 6 degrees F.

The embodiment also preferably has means for rinsing the ice mass 66with fresh water, and by allowing the mass 66 to melt, fresh water canbe produced. In this respect, as shown in FIG. 31, additional freshwater at room temperature, such as at 60 degrees F., can be sprayed downfrom nozzles 68 onto ice mass 66 to serve as a wash column, which helpsto remove the salty brine 67 from the ice mass 66 as the mass forms. Themajority of salt brine 67 is displaced from the spaces between the iceparticles 63 by gravity flow. For further removal of the brine thatattaches itself to the surface of each ice particle 63, there ispreferably an injection of fresh water on the layer of ice/brinedeposited at the base of crystallization chamber 41 to assist thegravity drainage of the salty brine 67 on a layer-by-layer basis. Thisfresh water freezes as it attaches to each layer and further displacesthe very thin viscous salty brine layer from the interstices between theice particles 63. The fresh water that is frozen on the ice particles islater thawed and preferably recovered for re-use without use ofadditional fresh water. If even higher purity water is required, adownstream wash column can be added.

Note that water spray can be introduced to assist in enhancing thegravity drainage of the salt brine 67 as a form of pre-wash. Because ofsurface tension, there may be some undesirable dissolved minerals andimpurities that are attracted to the surface of the ice crystals, andtherefore, it may become necessary to wash the ice mass with freshwater, such that it freezes onto the ice mass, and in the internalchannels and voids within the ice mass, as it releases the minerals andother impurities from the external and internal surfaces of the mass.The water preferably freezes onto the layer of frozen ice particles 63that are coated with brine, and, as the particles collect on the icemass 66, they displace the high viscosity brine from the surface of theice particle 63 and allow the salt brine 67 to flow to the outer surfaceof ice mass 66. The salty brine 67 is preferably drained out of thebottom of chamber 41, through a drain 69, as shown in FIGS. 31 and 32.

The bottom section 64 of the chamber 41 preferably comprises aperforated basket 71, which is able to catch the falling ice particles63, to form ice mass 66 thereon, but which allows the chilled air tocirculate out of chamber 41. In this respect, the side walls 72 ofchamber 41 preferably has channels or spaces 73 through which the excesschilled air can flow, wherein the excess chilled air preferably travelsout through an exit port 74, shown in FIG. 32, wherein the chilled aircan then be distributed to the air conditioning system and used aschilled air.

The right hand side of FIG. 32 shows how the ice particles 63 form atthe bottom of basket 71, to from a larger ice mass 66, or, in somecases, a slurry 74, wherein the perforations in the basket allow thesalty brine 67 to pass through, leaving behind the pure water iceparticles 63 in basket 71. Then, by removing the basket 71, the purewater ice mass 66 and/or slurry 74 can be removed from chamber 41.

The ice mass 66 of ice particles 63 which is removed with basket 71 canthen be melted, to produce fresh water at the bottom of a holding tank76, as shown in FIG. 33. As shown, fresh water 75 at relatively warmtemperatures, in this case, at plus 60 degrees F., can be sprayed downlike a wash column onto the ice particles 63, to rinse the ice, andcause the ice to melt. As shown in FIG. 34, local warm air 81 can alsobe brought into holding tank 76, to further assist in melting the iceparticles 63. As the ice melts, the fresh water droplets 78 pass throughthe perforations in basket 71, and collect at the bottom 77 of holdingtank 76, in the form of chilled fresh drinking water. More than onebasket 71 can be used so that the desalination and melting processes donot need to be interrupted while removing each basket 71 from chamber41.

Because the ice mass 66 is made of ice, and therefore, is cold, thefresh water that is produced when it melts will be chilled water. Theice is preferably at about minus 6 degrees F., and by passing water atabout 60 degrees F. over the ice, the resultant fresh water ispreferably at about 40 degrees F. From there, the fresh chilled watercan be distributed for drinking purposes, or through outlet 79 to aseparation tank, and stored there for later use by the air conditioningsystem, or, through outlet 80 to be re-circulated back to thecrystallization chamber 41 to be used as the spray 68 for the washcolumn, or spray 75 in holding tank 76. In either case, the water can beused for secondary purposes, including providing cooling for an airconditioning system, or washing the ice particles 63 in thecrystallization chamber 41, before the water is cycled back to bedistributed as fresh drinking water 52.

Thus the desalination system has means for separating the ice particles63 from the salty brine 67, to make sure that any left over salt orother impurity are removed from the ice particles. For example, theseice particles 63, which are preferably cooled to about minus 6 degreesF., to assure the formation of the solid ice phase and liquid brinephase, are preferably distributed into holding tank 76, or othercontainer, and sprayed by or otherwise mixed with additional fresh water75, such as water that had previously been purified by the system (whichcan be at room temperature), and then allowed to melt. By mixing thesuper cooled ice particles 63 with the additional water 75 at roomtemperature, the system is able to produce very cold fresh drinkingwater, i.e., at or near freezing temperatures.

F. Heat Exchange Built into Chamber Walls:

In the preferred embodiment, the chamber walls are preferably heatedwith the indrawn warm seawater and/or heated compressed air from thecompressor, to keep ice from collecting on the walls, and the ice massfrom sticking thereto. This way, when the ice mass is of a sufficientsize, it can be removed easily from the chamber and allowed to melt in awarm ambient environment to produce pure water, i.e., in a batchprocess.

In the preferred embodiment, the chamber walls are preferably adaptedwith pipes and/or cavities such that the indrawn seawater and/or heatedair from the compressor can be passed through the chamber walls. Thiseffectively serves as a heat exchanger which not only keeps the chamberwalls relatively warm to 1) prevent the ice from collecting on thewalls, 2) prevent the ice mass from sticking thereto, and 3) helpsregulate the temperature in the chamber, but it also helps to reduce thetemperature of the seawater before it is introduced into the chamber,and cool the compressor. This dual heat exchange effect enables both thetemperature of the chamber and the seawater to be regulated withouthaving to use any extra energy. The pipes are preferably extended aroundthe chamber to increase energy transfer efficiency between the seawaterand/or heated air, on one hand, and the chamber, on the other hand. Acavity can also be used, which is essentially a space between an innerwall, and an outer wall, i.e., the chamber can be made with a doublewall, so that seawater and/or heated air can be passed through theinside of the wall. This improvement that can be used in connection withthe batch process and relates to the use of pipes and/or cavities aroundthe chamber walls, which helps regulate the temperature in the chamber,but also the temperature of the seawater and/or air passing through thepipes.

G. Ice Mass Formation:

As the ice particles form and drop to the bottom of the chamber, theypreferably begin to coalesce and form an ice mass, which has theappearance of snow, more than an ice block, on top of the collectingsalt brine. This ice mass has relatively low density due to numerous airchannels and voids therein, and the porous nature of its formation. Thedensity of this mass is typically in the range of 0.5 to 0.6 g/cc,(recall that fresh fallen snow has a density of <0.1 g/cc) which isalmost half that of pure ice. A careful inspection of the mass revealsthat it looks more like snow, and has a network of channels and voidswhich allows any excess brine collecting on the ice particles to easilyrunoff and be drained through the mass and into the brine collection.And by keeping the ice mass, and the chilled air flow around the airmass, at somewhat warmer than the eutectic temperature, the salt brinethat attaches to the ice crystals can easily be washed away, i.e., theywon't form solid salt crystals.

As the ice mass grows, a consistent flow of the brine solution willcontinue to flow and drain down through the channels, voids and pores,to enable the brine to be further removed, and the ice mass to befurther purified. In this respect, it is worth noting that the actualice mass of fresh water itself will remain at about 0 degrees C. or 32degrees F. due to the significant amount of heat generated that isassociated with the phase change.

At first, due to the density difference between the freezing seawaterdroplets, and the seawater at the bottom of the chamber, the iceparticles will begin to float. As shown in FIG. 23, when the liquidwater forms ice, there is about a 9% drop in density, and, when thehigher salt concentrations of liquid seawater at near eutecticconditions causes the ice to form, there is a 71% drop in density andthe ice becomes strongly buoyant for a faster separation. Note that thesalt water solution at 24% concentration is 80 pounds per cubic feet. Insuch case, the ice readily separates from the saltwater solution. FIG.24 shows density variations for saltwater as a function of percentage ofsodium chloride.

After sufficient time has passed for the ice particles to accumulate,and the ice mass to form, which, in one embodiment under consideration,is two hours, but can also be as short as 10 minutes, or less, the verysmall ice crystals begin to float to the top of the dense saline liquidand coalesce to form an ice mass. But as the newly arriving dropletsrepeatedly land on the ice mass, the mass can form a rough uppersurface, with small hills and valleys. This can cause additionaldroplets falling onto the middle of the block to separate into salinedroplets and ice crystals inside the valleys. If the ice mass was solid,this could cause some of the liquid saline droplets to be suspended andtrapped in the ice block, because the ice mass typically forms withchannels and voids therein, the brine solution tends to seep downthrough the mass, and into the brine collection.

Nevertheless, to ensure that more of the ice particles tend to form inthe center, the nozzles can be positioned with a dense cluster patterncloser to the settling chamber centerline, as shown in FIGS. 17 and 18.The ice buildup will then occur preferentially toward the center of thechamber, forming an inverted cone or conical shape ice mass.Accordingly, as each new combined saline droplet attaches externally toa crystal of ice, they will attach to the cone-like surface of the mass,and the liquid saline droplet will flow over its containment surface, ifany, and run down the conical slope to the solution at the bottom.Another alternative is to use the above pattern of nozzle placements,but also control the flow through the nozzles so that the nozzledepositing at the centerline of the settling chamber has the highestflow rate and the longest flow time.

The ice mass, when removed, must still be washed to sweep away any saltand other minerals and impurities at the interface. When the ice mass isremoved from the chamber area to a temperate zone, it will melt to formpure water.

The fundamental mechanism for the attachment of the concentratedsolution of the salt to the frozen water is surface tension. Thus, allthe concentrated solution in the center of an open channel within theice mass will behave like a bulk liquid and drain out. On the otherhand, the few molecules of salt solution that attach to the ice stick tothe ice because of surface tension. The surface tension is released whenfresh water engages this sticky layer, freezes onto the ice and forcesthe sticky layer to be rejected and washed away. In the proposedcrystallization chamber, as the frozen particles (coated with highdensity liquid brine) accumulate on the top of the previous layers in aconical heap, a low flow rate of fresh water is preferably sprayed ontop of the most recently deposited layer. This fresh water deposits ontothe ice mass and releases the very thin brine layer from the surface ofthe ice/snow. Thus there is gravity flow of brine and also washed(flushed) brine that flows from the conical shaped mass of ice.

The spray of chilled fresh water onto the mass of ice/snow is frozenonto the mass of ice/snow as each layer is deposited. The freezing freshwater displaces the brine that is attached to the surface of theice/snow and releases the brine to drain through the crevices. When thewashed ice/snow mass is recovered and thawed, the sprayed fresh water isrecovered for reuse while the cleaned fresh water is used as product.

Porosity of the ice particles and the ice mass is an important parameterin the proposed process. Fortunately, it is a natural phenomenon for iceparticles to have high porosity. The porous channels and voids withinthe ice structure allow residual trapped brine to drain, especiallyduring the washing phase of the process. The residual contaminationwithin the clear water is therefore minimized and reduced to a levelthat is acceptable for drinking.

Consider that ice has a density of 0.92-gm/cc and water has a density of1.0-gm/cu cm so that ice floats on water. But more importantly there hasbeen an old assumption that snow is about 10% as dense as water, or0.10-gm/cc. It has been shown by measurement that at colder temperaturesthe snow forms an even more porous structure. See FIG. 6 which shows acomparison of the density of snow compared to air temperature.

H. Sample Calculation:

The following calculation shows the airflow requirements to generate12,000 gallons per day of fresh water from 13,793 gallons per day ofseawater processing. In this example, a 535 HP, two-stage turbo expanderoperating at an 85% thermodynamic efficiency is used, which will output24,155 pounds of chilled air at minus 168 degrees F. This chilled airwill absorb 939,146 BTU/HR if warmed to minus 6 degrees F., the eutectictemperature of saltwater. CHILLED AIR 535.07 HP 9.9 SCFM/HP FLOW5,297.15 SCFM FLOW 24,155.00 #/HR SPECIFIC HEAT 0.24 BTU/(# F.) TEMPINPUT −168 F. TEMP OUTPUT −6 F/ (939,146.40) BTU/HR

To show why it may be necessary to pre-cool the seawater to about 30 to40 degrees F., the following analysis will begin by using a 60 degree F.saltwater at 64 pounds per cubic feet, which will be chilled to minus 6degrees F. based upon the approximate calculation: SEAWATER FLOW 4917#/HR SPECIFIC HEAT 1 BTU/(# F.) TEMP INPUT 60 F. TEMP OUTPUT 32 F.FUSION 144 BTU/# SPECIFIC HEAT 0.5 BTU/(# F.) TEMP INPUT 32 F. TEMPOUTPUT −6 F. 939,147.00 BTU/HR

In this example, a relatively small 4 feet diameter crystallizationchamber is used, wherein a flow of chilled air of 5,297 SCFM is injectedinto the chamber at a velocity of 7 feet per second vertically downward.The example 4,000-micron spherical droplet size has a vertical settlingvelocity of 44 feet per second in still air. Thus there is a 7 ft/sec+44ft/sec=51 ft/sec downward vertical transport of the droplet. If thechamber is 8 feet tall, there is a less than 8/51 second residence timein flight. Note: The above sizes of the chamber, droplets, etc., and thespeed of the airflow, falling velocity of droplets, etc., areapproximate, and may be deviated to the extent necessary, by taking intoaccount the factors discussed herein. Thus it may be necessary toconsider pre-chilling the saltwater intake from 60 degrees F. down toabout 30 degrees F., before the saltwater is injected into the chamber,such as by forcing the intake water to circulate around thecrystallization chamber, as will be discussed.

It is recognized that the seawater droplets will have to be super cooledto minus 26 degrees F. rather than minus 6 degrees F. to actuallyinitiate the ice (fresh water) formation. The time delay for theinitiation of the ice formation is shortened when the air temperature ismuch colder than minus 26 degrees F. For this reason, the present systempreferably begins with a chilled air temperature of minus 135 degrees F.to minus 175 degrees F., give or take, or any temperature that worksgiven the factors discussed herein. When the ice (fresh water) starts toform, it forms in less than a few seconds. Thus it is necessary for thedroplets to initiate their freezing process in the crystallizationchamber using a large sub-cooling temperature difference to start thesolidification process while falling as a droplet, but to complete thefreezing process after it has deposited on the growing mound of ice atthe bottom of the chamber.

In some circumstances, the outer surface of the 4,000-micron diameterdroplet may drop to temperatures far below the eutectic temperature andform fresh water ice, salt crystals and salt crystals with each moleculeof NaCl attached to two molecules of water. There will also bemetastable liquids in that mixture of solids. However, when warmed toslightly above the eutectic temperature, the thermodynamic mixture offresh water ice and separate high density and high concentrationsaltwater solution becomes established as per the equilibrium diagram.

It is expected that the droplet will experience a freezing environmentfor a fraction of a second to only a few seconds in downward verticalflight and a freezing environment from between 10 seconds to 10 minutesor more in the accumulated mass at the bottom of the crystallizationchamber. For the batch process of say 6 to 10 minutes, there ispreferably more than enough time to attain equilibrium conditions in themixture once the ice mass begins to form, to configure itself accordingto the phase diagram.

When the saltwater temperature remains at slightly warmer than minus21.12 degrees C. (251.8 degrees K), or minus 6.02 degrees F., the totalsaltwater separates into two phases: (1) Pure ice when later thawedbecomes pure water, and (2) Concentrated liquid saltwater solution. Theice (lower density) floats atop the high-density concentrated saltwater. This is the desired state. FIG. 20 shows the equilibrium phasediagram for a mixture of sodium chloride (NaCl and water. The sodiumchloride is called the solute and the water is the solvent. When thetwo-phase region is entered at cold temperatures, there develops twophases (1) pure solid ice and (2) liquid brine with salt crystal as thesolute and liquid water as the solvent.

When the saltwater temperature remains at colder than minus 21.12degrees C., or minus 6.02 degrees F., the saltwater separates into threephases: (1) Pure ice when later thawed becomes pure water, (2) Saltcrystals wherein there are two water molecules attached to each saltcrystal (NaCl*2H₂O) and (3) Pure salt crystals. Although the equilibriumdiagram only shows these three configurations at temperatures belowminus 6 degrees F., there are other metastable liquid states that existin this less than minus 6 degrees F. regime. This is an undesired statefor our operation.

The data for a seawater sample (for which [Na+]) 0.46 M) are also shown;the high liquid fraction for this sample below the eutectic point ispresumably due to the presence of other salts that have a lower eutecticthan NaCl (in particular, MgSO4 and MgCl2). For the 0.5 M sample(-seawater) more than 99% of the NaCl precipitates as NaCl*2H2O at theeutectic point, but for the more dilute samples typically more than halfof the initial Na+ remains in a free ionic state to as low as 228 K.

According to an idealized interpretation of the Gibbs phase rule and thephase diagram of NaCl and water, NaCl(aq) solutions solidify completelyat temperatures below the eutectic point (252° K or −6° F.) to a mixtureof (1) pure water ice, (2) NaCl(solid), and (3) NaCl*2H₂O(solid), forall initial salt concentrations. The finding that a liquid brine phasecan coexist with large amounts of ice and solid sodium salts attemperatures more than 20 degrees K below the eutectic point wouldtherefore represent an apparent deviation from ideal equilibriumbehavior. To differentiate this unfrozen brine phase from the“quasi-liquid layer” (QLL) previously found in studies of bulk purewater ice, we refer to the solution phase as a “quasi-brinelayer”, orQBL.

The coexistence of a liquid brine phase with pure ice at temperaturesbelow the eutectic point is indicated in experiments reported byThurmond and Brass¹⁷ and Koop et al.¹⁸ Using differential scanningcalorimetry (DSC), Koop et al. observed two separate thermal emissionevents during cooling of dilute NaCl solutions, which they attributed tothe supercooled-liquid to solid-phase transitions associated with (1)the formation of pure ice (pure solid water) and (2) the precipitationof NaCl*2H₂O. The temperatures of these two-phase transitions convergeas the NaCl concentration increases and become essentially equal forconcentrations above 16 wt % NaCl.

When the saltwater solution is progressively chilled to the freezingtemperature of pure water, then to the eutectic temperature of NaCl andthen to colder temperatures other metastable compounds form describedabove as QLL and QBL. Thus it is expected that when the droplets fromthe spray nozzle encounter super chilled air, that pure ice (pure frozenwater) will form with a series of other NaCl crystal and waterstructures. However, as the droplet warms back up to slightly above theeutectic temperature, the equilibrium solid ice and concentrated NaClsolution forms that is associated with the usual equilibrium diagram forthe salt solution.

FIG. 19 shows this hysteresis loop and return to the initial condition.Time proceeds in the direction indicated by the arrows; the freezingtemperature (T_(f)) and the eutectic temperature (T_(e)) are shown bythe dashed vertical lines. When the liquid brine is first cooled (C1),no phase transition is observed, and thus the liquid is metastable belowT_(f). During cooling C2, pure ice suddenly precipitates, evolving heat,and the liquid fraction drops, but not to zero. The remaining MBL iscooled during C3 until a second phase transition occurs (C4), resultingin a second exothermal event and a drop in the liquid fraction. A liquidphase, the QBL, nonetheless remains, as revealed by the NMR experiments,and can be cooled during C5. Upon warming (W1), the liquid fractiongradually increases until Te is reached, whereupon rapid melting beginsand the liquid fraction jumps. This sudden melting stops when theresulting brine reaches the approximate concentration dictated by thefreezing point depression curve, and the liquid fraction rises smoothlythereafter as the temperature is raised (W3) and melting continues. Notethat these discussions were taken from “NMR Investigation of theQuasi-Brine Layer in Ice/Brine Mixtures” by Cho, Shepson, Barrie, Cowinand Zaveri.

This discussion indicates that there can be sufficient heat transferfrom the chilled air from the turbo expander in the pipes and/orcavities, and the intake seawater in the pipes and/or cavities, to haveboth fluids reach their equilibrium temperature of minus 6 degrees F.(or close to it) prior to injection of the seawater through a nozzleinto the crystallization chamber. Of course, it would be necessary forthe pipes and/or cavities to be joined together along a common surfacefor best heat exchange. The pipes and/or cavities and the chamber wallsare preferably made of materials with excellent heat exchangeproperties, i.e., aluminum, copper, etc. The flow requirement in thepipes and/or cavities is such that the super cooled state of the liquidbrine is sustained until it is sprayed into the crystallization chamber.The only reason for the droplet formation is to permit the solid brineto form liquid brine and be forced to the outside of the ice droplet.The success of this approach would result in a minimum sizecrystallization chamber of interest to users who are cramped for space.

The phase change occurs within less than a few seconds so that theresidence time of the droplet in the chilled air and on the depositedmound of ice need only be less than a few seconds (FIG. 19). Theprogress of freezing could be followed at short intervals by rapidlyscanning the liquid water 1H NMR line and monitoring its disappearanceas the temperature dropped below phase transition points. Most solutionsin the present study were found not to begin solidifying until thetemperature was reduced below 257° K (or +3.2° F.). Recall that theeutectic temperature is minus 6 degrees F. Once freezing begins, theprocess was rapid, with the largest changes in the NMR signal completewithin a few seconds.

Saltwater from the sea, at the seawater temperature (say 60 degrees F.),is filtered and pumped through the pipes and/or cavities that surroundsthe bottom surface and the sidewalls of the crystallization chamber. Thewarm seawater circulates the warm intake seawater in a direction thatwarms the bottom surface initially and finally warms the sidewalls ofthe chamber prior to being sprayed through the nozzle into thecrystallization chamber. Thus there are two important effects:(1)Saltwater sprayed into the crystallization chamber is pre-chilled to 30to 40° F. before it comes into contact with the chilled air inside thecrystallization chamber, and (2) The bottom surface and the sidewalls ofthe crystallization chamber are sufficiently warm to prevent any icebuildup.

The outermost boundary of the nozzle spray is limited radially so thatlittle or no saltwater droplets strike the sidewalls, even as the heightof the deposited ice increases with time. The droplets from the sprayerproduce a range of seawater droplet sizes preferably with most all ofthe droplets centered around 4,000 microns in diameter. This occursbecause of the size of the orifice in the showerhead and the pressuredifference. It is also possible to select 1,000 microns in diameterseawater droplets, and even 250 microns diameter seawater droplets, orother size.

The droplet preferably starts at between 30 degrees F. and 40 degrees F.and comes into contact with the chilled air, preferably at minus 121degrees F. or colder. FIG. 21 shows the core temperatures of thedroplets after 0.2 seconds of exposure to minus 121 degrees F. ofchilled air. The surface of the droplet will immediately attain atemperature slightly warmer than minus 121 degrees F. It is assumed thatthe heat transfer coefficient for the air/water interface is 1 to 5BTU/(Hr Sq-Ft F) for free convection. If this flow conforms more toforced convection, the heat transfer coefficient will be higher and thecore temperatures will be colder.

However, the core temperatures of the large 4,000 micron diameterdroplet will be +24° F. and +32° F. for heat transfer rates of h=5BTU/(Hr Sq-Ft F) and 1 BTU/(Hr Sq-Ft F), respectively, in 0.2 seconds offlight (First two columns of FIG. 21). There is no freezing in thisshort time. However, there is still the case wherein a credible higherheat transfer coefficient just may bring in these core temperatures tolower values. If the lumped mass model being used here is abandoned, itis expected that the actual freezing process will take place from theoutside to the inside so that a frozen ice shell forms. The first twocolumns of FIG. 22 show that the freezing of the entire droplet willtake place about 2 seconds after deposition. The chilled air has only ashort residence time in the downward flight, and will need about 2seconds more to completely surrender its stored chilled energy after thedroplet has been deposited

However, the core temperatures of the 1,000 micron diameter droplet willbe −56.6° F. and +7.8° F. for heat transfer rates of h=5 BTU/(Hr Sq FtF) and 1 BTU/(Hr Sq Ft F) in 0.2 seconds of flight (Third and fourthcolumns of FIG. 21). Thus the freezing of the entire droplet will takeplace about 2 seconds after deposition. Thus the chilled air has only ashort residence time in the downward flight, and will need about 2seconds more to completely surrender its stored chilled energy after thedroplet has been deposited (see third and fourth columns of FIG. 22).

It is obvious that if 250-micron droplets are used, that even shorterflight times in the crystallization chamber will freeze the dropletscompletely.

It is important to note that these calculations assume that the −121° F.is maintained for the entire downward flight. Recall that heat exchangehas been taking place with the incoming seawater in the pipes and/orcavities and during the heat exchange with the seawater droplets duringits downward flight. The heat exchange is complete when the air and thetwo-phase mixture attain minus 6 degrees F.

If very small droplet sizes are used, much of the freezing will stilltake place after deposition. Portions of the droplet will be supercooled at the outside radius of each droplet and these super coolregimes will contain metastable structures. But at equilibrium, afterdeposition, the ice particles will pack together and they will floatatop the dense brine. When the brine drains from the ice mass, voidswill form. Thus the propeller will move a frothy mass toward the exitplane.

I. Example of Proposed System:

An embodiment of the proposed system is described by showing snapshotsof the system configuration at six key times in its operation.

1. First Step:

The first step in the counter flow arrangement shown in FIG. 25 showsthe nozzle spraying the intake seawater into droplets at 70 degrees F.with a median diameter of 4,000 microns, and the chilled air introducedat 7,151 SCFM and temperature of minus 157 degrees F. The upwardvelocity of the droplets from the nozzle eventually reaches a minimumrelative velocity because of gravity, and then settles downward towardthe base of the column. The final mixture of (1) seawater droplets and(2) chilled air, results in minus 6 degrees F., the eutectic temperatureof the mixture. One can control the final mixture temperature so that itis warmer or colder than the eutectic temperature by adjusting the flowof intake seawater and chilled air.

2. Second Step:

As shown in FIG. 26, the mixing of the seawater droplets and chilled airoccurs with some droplets (1) Falling through chilled air with chilledice and seawater as one piece but with the ice separated from the saltsolution (2) Colliding and coalescing with nearby droplets andprogressing with the separation process within the new and largerdroplet, and (3) Droplets that reach the bottom pool of fluid so thatthe saline solution of the droplet merges with the larger pool of fluidand the released ice crystal buoys to the top where it may coalesce withother previous ice crystals.

As the newly arriving droplets repeatedly land on the ice mass, the masscan form a rough upper surface, with small hills and valleys. This cancause additional droplets falling onto the middle of the mass toseparate into saline droplets and ice crystals inside the valleys. Thiscould cause some of the liquid saline droplets to be suspended andtrapped in the ice mass, although studies show that channels and voidsare formed in the ice mass, through which the brine can pass down intothe collected solution.

To avoid this, and enable the saline liquid to run off the edges, thenozzles can be positioned with a dense cluster pattern closer to thesettling chamber centerline. The ice buildup will then occurpreferentially toward the center of the chamber, forming an invertedcone (see FIGS. 17 and 18). Accordingly, as each new combined salinedroplet attaches externally to a crystal of ice, they will attach to thecone surface, and the liquid saline droplet will flow over itscontainment surface, if any, and run down the conical slope to thesolution at the bottom. Another alternative is to use the above patternof nozzle placements, but also control the flow through the nozzles sothat the nozzle depositing at the centerline of the settling chamber hasthe highest flow rate and the longest flow time.

The injection height of the chilled air should be higher than the icemass, as discussed above in connection with FIG. 17, and means forproducing an annulus gap between the ice mass and chamber walls ispreferably provided, as discussed in connection with FIG. 18.

3. Third Step:

If too little seawater is sprayed into the settling chamber, the mixtureat the bottom of the chamber will fall below the eutectic temperatureand not only will there be solid ice going out of solution but the saltwill go out of solution and deposit itself as salt crystals. This isshown in FIG. 27. See conical shape of ice block of preferred embodimentin FIGS. 17 and 18.

4. Fourth Step:

The 2 hours of the continuous operation has come to an end and it istime to remove the ice block. The nozzle structure is moved to the side,and the solution is raised to the level where it does not spill over theedges of the chamber wall.

Over the two hour period the ice crystals collect on the top of thedenser saline solution and merge into an ice block. At this time theinterior contents of the entire settling chamber is moved upwards by ahydraulic piston until the top surface of the saline solution reachesthe top edge of the settling chamber. There is then access to the iceblock by pincers that hook the ice block and move it to the nextposition where it is scraped and washed, as shown in FIG. 28. Thechilled solution will be saved for later steps in the operation. Thesurfaces of block of chilled ice need to be scratched or rinsed withfresh water to remove any brine solution in its interfaces. It is thenleft in a tank for room temperature thawing and for later use as puredrinking water.

Alternatively, after the ice mound has built to its planned height andis floating on the concentrated salt solution, the saltwater drain atthe bottom of the crystallization chamber is opened to drain the saltwater. When the saltwater solution has been completely drained, thedrain is closed. The bottom drops down and swings from the horizontalposition to a vertical position around a hinge. The hinge supports thebottom surface of the crystallization chamber. Any pipes or tubingsurrounding the bottom surface of the chamber is preferably configuredto accommodate the pivot around the hinge. Then, the ice mound can slidedown the pivoted bottom surface and fall upon a conveyor belt. Theconveyor belt sends the ice mound to the tank containing previous icemounds that are thawing.

Since the transfer of the ice from the chamber is accomplished bygravity, the incoming chilled air can be adjusted to be about 14.67-psia(1 atmosphere pressure). This 14.67-psia exit pressure for the turboexpander and 200-psia for the entrance pressure to the turbo expander,permit extremely cold temperatures to be achieved at the turbo expanderexhaust into the crystallization chamber. However, this large pressuredrop will require a two-stage turbo expander.

5. Fifth Step:

The incoming warm seawater will be passed through a heat exchangercounter currently with the outgoing chilled briny water, as shown inFIG. 29. The energy savings will permit a higher desalination rate forthe same chilled airflow.

6. Sixth Step:

The operation of the system at slightly above the eutectic temperatureis convenient in that the dense saline solution floats the ice andTeflon can be provided on the inside surface of the chamber walls toavoid the ice block from sticking to the vessel. In the final stage,after the ice block is removed, it is convenient to drop the temperaturebelow the eutectic temperature to deposit the ice as crystals that canbe removed. This process will likely be initiated earlier than in thelast step.

As shown in FIG. 30, to remove the salt, the hydraulic lift is droppedto its initial position. There are then two conditions. (1) Thethermocouple indicates that the saline solution is slightly warmer thanthe eutectic temperature. In this case, when the saline solution isremoved, all the salt is removed with the saline solution. This chilledsaline solution is returned to the heat exchanger to precool the intakeseawater. (2) The thermocouple indicates that the saline solution isslightly colder than the eutectic temperature. The saline solution isdrained and processed as described in the first case. Thereafter, thehydraulic piston is dropped below the bottom level of the settlingchamber and the solidified salt is scraped off the piston surface. Thesalt can be discarded or a use found for it.

J. Comparison to Other Methods:

The following discussion is provided to show that the present method isable to produce fresh drinking water at a lower cost, i.e., pound perminute, than the previous desalination processes. The analysis belowdescribes the methodology and assumptions used to evaluate the utilityand efficiency of this method of desalinating seawater. The analysisbelow consists of two basic steps:

-   -   (1) Defining the thermodynamics of the process that involves        matching the cooling/freezing capacity of the chilled air, with        the energy required to be removed from the batch of seawater to        cause the salt and the pure water within the batch to        crystallize.    -   (2) Defining the setup and specifying the steps in the process        required to achieve physical separation of the salt and ice        crystals, and to accomplish desalination of the batch of        seawater.

As listed below, in this batch process the amount of seawater wasdetermined to be 11,000 pounds and the duration of the desalinationprocess of the batch was assumed to be 2 hours. The initial temperatureof seawater was assumed to be 70° F. The eutectic point of NaCl is −6.2°F. and the eutectic composition is 23.3%. The total amount of coolingrequired for this batch is 2,211,000 BTU. This includes the iceformation phase (163 BTU/# fusion). Ice Formation Included 120 min11,000 # salt water 1 BTU/(# F.) 70 F. 32 F. 163 BTU/# fusion @−6.2 degF. 2,211,000.00 BTU cooling required

If the ice formation phase is not included, supercooled water isachieved, and the available cooling capacity can accommodate 30,000 # ofsaltwater. No Ice Formation (SUPERCOOLED WATER) 120 min 30,000 # saltwater 1 BTU/(# F.) 70 F. −6.2 F. 0 BTU/# no ice 2,286,000.00 BTU coolingrequired 250 # salt water/min 0.857 fraction of fresh water 214 # freshwater/min

The 500 kW turbo expander processes 7,151 scfm of air and delivers theatmospheric pressure air at −153° F. for desalination. The temperatureof −6.2° F. is the eutectic temperature for ice formation and separationfrom salt crystals. Thus, we will use the air for desalination over thetemperature range of −153° F. to −6.2° F. The calculation shown belowgives the available cooling energy as 2,297,508 BTU if we operate theflow process for 120 minutes. The intake of 11,000 pounds of seawater at70° F. and bringing it to −6.2° F. requires 2,211,000 BTU. 500 kW(thermal) 670 hp 10.67 scfm/hp 7,151 scfm 120 min 858,177 scf 0.076 #/cuft 65,221 # air 0.24 BTU/(# F.) −6.16 F. −153 F. (2,298,508.17) BTUcooling available

The iteration of the above calculations for the 500 kW system shows thatthe proposed freeze crystallization will ideally produce 79.75 # freshwater per minute, ideally. Thus, 6.27 kW is required to produce a poundof fresh water per minute. This compares to the scraped surfacecrystallizer that requires 11.4 kW to produce a pound of fresh water perminute; and to the reverse osmosis membrane desalinator that requires68.2 kW to produce a pound of fresh water per minute.

The embodiments discussed and shown herein are merely exemplary and areby no means intended to be limiting. The present invention contemplatesvarious methods and systems that can be adapted that can carry out theintents and purposes of the invention, which may be a variation of theembodiments disclosed herein.

1. A system for desalinating seawater comprising: a compressor forcompressing air; an expander for expanding compressed air to co-generatechilled air; a chamber, with at least one nozzle through which theseawater can be sprayed into the chamber, and into which the chilled airfrom the expander can be introduced, wherein the exposure of theseawater to the chilled air enables ice particles consisting of purewater to be formed in the chamber; a device that helps remove the iceparticles from the chamber, thereby helping to separate the pure waterin the ice particles from the impurities in the seawater.
 2. The systemof claim 1, wherein the system comprises at least one of thefollowing: 1) a storage tank is provided to enable the compressed air tobe stored therein, and wherein the expander is adapted to release andexpand the compressed air inside said tank, to produce chilled air; 2)an electrical generator is provided which is adapted to produceelectricity as the compressed air is being released by the expander,wherein the chilled air is produced as a by-product of producingelectricity; 3) a surge tank, wherein, as the compressed air is expandedby the expander, the energy produced thereby is used to drive a secondcompressor that produces additional compressed air energy that can beintroduced into the surge tank; 4) at least one heat exchanger forhelping to reduce the temperature of the compressed air before it isexpanded by the expander; or 5) at least one common shaft between thecompressor and expander which allows them to operate in association witheach other.
 3. The system of claim 1, wherein the temperature of thechilled air introduced into the chamber is below the eutectictemperature for the seawater, and wherein the ice particles are allowedto deposit at the bottom of the chamber in the form of a mass, whereinthe temperature of the mass at the bottom of the chamber is above theeutectic temperature for the seawater.
 4. The system of claim 3, whereinthe temperature of the chilled air is between minus 135 degrees F. and175 degrees F., and the temperature of the mass of ice particles isabove minus 6.2 degrees F., such that a liquid brine consisting of theimpurities in the seawater can runoff from the mass.
 5. The system ofclaim 1, wherein the system comprises at least one of the following: 1)the system is adapted such that the seawater can be sprayed down intothe chamber from above, and the chilled air can be introduced such thatit flows upward inside the chamber; 2) the system is adapted such thatthe seawater can be sprayed down into the chamber from above, and thechilled air can be introduced such that it flows downward inside thechamber in the same direction as the seawater.
 6. The system of claim 1,wherein chilled air is introduced at a temperature between minus 135degrees F. and 175 degrees F.
 7. The system of claim 1, wherein said atleast one nozzle is adapted and configured to produce a centrallyfocused spray of seawater that tends to keep the droplets that areformed by the spray away from the outer walls of the chamber, and towardthe center of the chamber, wherein as the ice particles fall, they tendto land near the center of the chamber, to form an ice mass which allowsthe seawater to flow down the sides of the ice mass, without beingcaptured within the ice mass formation as it coalesces and freezes. 8.The system of claim 1, wherein the walls of the chamber are adapted withtubes or passages which allow the seawater to be circulated therein, tohelp regulate the temperature of the walls within the chamber.
 9. Thesystem of claim 8, wherein the seawater is passed through the tubes orpassages in the chamber walls to help warm up the chamber walls, and inturn, the cold temperature inside the chamber can help pre-chill theseawater as it circulates before being sprayed into the chamber, whereinthe seawater that is introduced into the chamber is pre-chilled to lessthan 40 degrees F.
 10. The system of claim 1, wherein the walls of thechamber are adapted with tubes or passages which allow heated air fromthe compressor to be used to regulate the temperature of the wallswithin the chamber.
 11. The system of claim 10, wherein the heated airis passed through the tubes or passages in the chamber walls to helpwarm up the chamber walls, wherein the cold temperatures inside thechamber can help pre-chill the heated air as it circulates to theexpander.
 12. The system of claim 1, wherein the location where thechilled air is introduced into the chamber is above the height that isexpected to be reached by an ice mass formation that is formed withinthe chamber when the ice particles coalesce and freeze together at thebottom of the chamber.
 13. The system of claim 1, wherein a heater isprovided in connection with the walls of the chamber near where the iceparticles accumulate, wherein the walls of the chamber can be heated toprevent the ice particles from freezing on the walls, and/or to allowany ice mass that is produced as the ice particles coalesce and freezewithin the chamber to be easily removed.
 14. A method of desalinatingseawater comprising: compressing air to produce compressed air energy;releasing the compressed air with an expander to co-generate chilledair; introducing the chilled air into a chamber; spraying the seawaterin the form of droplets into the chamber; exposing the seawater dropletsto the chilled air within the chamber, thereby forming ice particlesconsisting of pure water within the droplets; and forming a mass withthe ice particles within the chamber, thereby helping to separate thepure water in the ice particles from the impurities in the seawater. 15.The method of claim 14, wherein the method comprises at least one of thefollowing: 1) storing the compressed air energy in a storage tank beforereleasing the compressed air energy; 2) co-producing electricity using agenerator, as the compressed air is being released by the expander,wherein the chilled air is produced as a by-product of producing theelectricity; 3) using the compressed air energy to drive a supplementalcompressor that produces additional compressed air energy that can beintroduced into a surge tank; 4) using at least one heat exchanger toreduce the temperature of the compressed air before it is expanded bythe expander; or 5) using at least one common shaft between thecompressor and expander to allow them to operate in association witheach other.
 16. The method of claim 14, wherein introducing the chilledair comprises introducing chilled air at below the eutectic temperaturefor the seawater, and wherein forming the mass of ice particlescomprises keeping the temperature of the mass at the bottom of thechamber above the eutectic temperature for the seawater.
 17. The methodof claim 16, wherein the temperature of the chilled air is between minus135 degrees F. and 175 degrees F., and the temperature of the mass ofice particles is above minus 6.2 degrees F., such that a liquid brineconsisting of the impurities in the seawater can runoff from the mass.18. The method of claim 14, comprising at least one of the followingsteps: 1) spraying the seawater down into the chamber from above, andintroducing the chilled air such that it flows upward inside thechamber; 2) spraying the seawater down into the chamber from above, andintroducing the chilled air such that it flows downward in the samedirection as the seawater being sprayed into the chamber.
 19. The methodof claim 14, wherein said at least one nozzle is adapted and configuredto produce a centrally focused spray of the seawater that tends to keepthe droplets that are formed by the spray away from the outer walls ofthe chamber, and toward the center of the chamber, wherein as the iceparticles fall, they tend to land near the center of the chamber, toform an ice mass which allows the seawater to flow down the sides of theice block, without being captured within the ice mass formation as itcoalesces and freezes.
 20. The method of claim 14, wherein the methodcomprises circulating the seawater through at least one tube or passagewithin the chamber walls to help warm up the chamber walls, and in turn,cause the cold temperature inside the chamber to help pre-chill theseawater before being sprayed into the chamber, wherein the seawaterthat is introduced into the chamber is pre-chilled to less than 40degrees F.
 21. The method of claim 14, wherein the method comprisescirculating heated air from the compressor through at least one tube orpassage in the chamber walls to help warm up the chamber walls, whereinthe cold temperatures inside the chamber can help pre-chill the heatedair as it circulates to the expander.